Function generator, crystal oscillation device and method of adjusting crystal oscillation device

ABSTRACT

A temperature compensating crystal oscillation device includes a constant voltage circuit ( 12 ) for outputting a predetermined voltage independent of the ambient temperature, a temperature sensor circuit ( 13 ) for outputting a voltage in proportion to the ambient temperature, and a control circuit ( 14 ) for receiving the constant voltage output from the constant voltage circuit ( 12 ) and the voltage output in proportion to the temperature from the temperature sensor circuit ( 13 ) and for generating a control voltage (Vc) used for compensating a temperature characteristic of a quartz oscillator in the entire range of the ambient temperature through polygonal lines approximation of a negative cubic curve by using continuous lines. Furthermore, the crystal oscillation device includes a VCXO ( 15 ) whose oscillation frequency is controlled to be a predetermined value by the control voltage (Vc), and a ROM/RAM circuit ( 16 ) for storing temperature compensating parameters used for compensation of a temperature characteristic of the control voltage (Vc) for optimizing the oscillation frequency of the VCXO ( 15 ).

TECHNICAL FIELD

The present invention relates to a function generator for generating acontrol signal for compensating temperature dependency of an oscillationfrequency output from a crystal oscillation device, a crystaloscillation device using the function generator and a method ofadjusting the crystal oscillation device.

BACKGROUND ART

Recently, there is a sharp rise in demand for portable electronicequipment, and a compact and accurate crystal oscillation device forgenerating a reference clock signal is indispensable to such electronicequipment.

The oscillation frequency of a crystal oscillator in a crystaloscillation device has a temperature characteristic including cubic andlinear components derived from a quartz oscillator used in the crystaloscillator. Specifically, with the abscissa indicating the ambienttemperature T_(a) and the ordinate indicating the oscillation frequencyf as is shown in FIG. 26(a), the oscillation frequency f of a crystaloscillator whose temperature characteristic is not compensated isrepresented as a substantially cubic curve 101 with a difference ofapproximately 10 ppm through 30 ppm between the maximum value and theminimum value. Herein, the ambient temperature T_(a), is assumed to beapproximately −30° C. through +80° C. Accordingly, when an ideal controlvoltage curve 102 as is shown in FIG. 26(b), with the abscissaindicating the ambient temperature T_(a) and the ordinate indicating acontrol voltage Vc, is generated and applied to the crystal oscillator,df/dT_(a) can be zero and the oscillation frequency f can besubstantially independent of the temperature as is shown in FIG. 26(c).

The temperature characteristic can be compensated, for example, asfollows: A varactor diode (i.e.,a variable capacity diode) serving as afrequency adjustment device is connected with the crystal oscillator,and a control voltage having a cubic and linear temperaturecharacteristic for compensating the temperature characteristic of thecrystal oscillator is applied to the varactor diode. Thus, thetemperature characteristic of the oscillation frequency can bestabilized.

Actually, it is technically very difficult to generate a control voltageVc having the ideal temperature characteristic as is shown in FIG.26(b). Therefore, in general, a control voltage having a pseudo cubictemperature characteristic is generated by any of various methods so asattain the temperature compensation of the oscillation frequency.

Now, a conventional temperature compensating crystal oscillation devicedisclosed in Japanese Laid-Open Patent Publication No. 8-288741 will bedescribed with reference to accompanying drawings.

FIG. 27 shows the functional block configuration of the conventionaltemperature compensating crystal oscillation device. In the temperaturecompensation of this crystal oscillation device, the cubic and lineartemperature characteristic of the crystal oscillator is divided intoplural temperature regions, and voltages in the respective dividedtemperature regions represented as a function of the temperature aresubjected to polygonal lines approximation to obtain temperature lines.

Specifically, a memory 111 of FIG. 27 stores each divided temperatureregion, a temperature coefficient (proportional coefficient) of thetemperature line in the temperature region, and a voltage value at roomtemperature on the temperature line of each region of the voltage line.Voltage line data corresponding to the ambient temperature detected by atemperature sensor circuit 112 is selectively read from the memory 111,and a predetermined control voltage is generated in an amplifier circuit113 on the basis of the read control voltage data. The thus generatedcontrol voltage is applied to a voltage control crystal oscillator 114,so that the oscillation frequency can be stabilized through thetemperature compensation of the oscillation frequency.

Furthermore, as is shown in FIG. 28(a), the temperature sensor circuit112 performs the polygonal lines approximation by using A/D conversion.Therefore, frequency skip, namely, temporary discontinuity of thevoltage lines, is caused between temperature regions as is shown in FIG.28(c). In order to avoid this frequency skip, a sample and hold circuit115 is interposed between the amplifier circuit 113 and the voltagecontrol crystal oscillator 114, so as to make the frequency varysmoothly with time.

However, since such a conventional temperature compensating crystaloscillation device uses the A/D conversion for the polygonal linesapproximation for generating the control voltage to be used for thetemperature compensation, a quantum noise is unavoidably caused, and thefrequency skip cannot be avoided in principle. Moreover, a clock signalgenerator is indispensable, and hence, there arises a problem of a clocknoise. In addition, it disadvantageously takes time to stabilize theoscillation frequency after the actuation due to a time constant of thesample and hold circuit 115.

Furthermore, in measurement and adjustment of the temperaturecharacteristic, the temperature characteristic of the oscillationfrequency of the crystal oscillation device is measured with the ambienttemperature changed discretely in order to compensate the temperaturecharacteristic. Therefore, an error can be caused in the adjustmentitself. In order to reduce the error, it is necessary to increase thenumber of the divided temperature regions, which leads to anotherproblem that the storage capacity of the memory 111 is increased.

The object of the invention is eliminating the frequency skip from thecontrol voltage itself and easing the adjustment of the temperaturecompensation.

DISCLOSURE OF INVENTION

In order to achieve the aforementioned object, a control voltage fortemperature compensation is generated in this invention by using merelyanalog circuits free from frequency skip in principle.

The function generator of this invention for generating a control signalas a function of a temperature, comprises a first analog signalgenerating circuit for generating and outputting a predetermined analogsignal independent of an ambient temperature; a second analog signalgenerating circuit for outputting an analog signal dependent upon theambient temperature; and a control circuit for receiving the signal fromthe first analog signal generating circuit and the signal from thesecond analog signal generating circuit, and for generating, with afeasible range of the ambient temperature continuously divided into afirst temperature region, a second temperature region, a thirdtemperature region, a fourth temperature region and a fifth temperatureregion in this order along a direction from a low temperature to a hightemperature, control signals respectively corresponding to the fivetemperature regions, wherein the control circuit outputs a first controlsignal whose output value is varied in proportion to increase of thetemperature at a first change rate when the ambient temperature is inthe first temperature region; a second control signal whose output valueis continuous with the first control signal and is a predetermined valueindependent of the temperature when the ambient temperature is in thesecond temperature region; a third control signal whose output value iscontinuous with the second control signal and is varied in proportion toincrease of the temperature at a second change rate when the ambienttemperature is in the third temperature region; a fourth control signalwhose output value is continuous with the third control signal and is apredetermined value independent of the temperature when the ambienttemperature is in the fourth temperature region; and a fifth controlsignal whose output value is continuous with the fourth control signaland is varied in proportion to increase of the temperature at a thirdchange rate having the same polarity as the first change rate.

Thus, the function generator of this invention includes the first analogsignal generating circuit for generating and outputting thepredetermined analog signal independent of the ambient temperature, thesecond analog signal generating circuit for generating and outputtingthe analog signal dependent upon the ambient temperature and the controlcircuit for receiving the signal from the first analog signal generatingcircuit and the signal from the second analog signal generating circuitand for generating the control signals continuously corresponding to theentire regions ranging from the low temperature to the high temperature.Accordingly, although the ambient temperature is divided into the fiveregions, the frequency skip is not caused in the vicinity of theboundary between the regions, resulting in attaining good approximationwith a small approximation error. Moreover, since the function generatorincludes the analog circuits alone, a clock generator is not requireddifferently from a digital circuit, and hence, a clock noise can also beavoided.

Furthermore, when the ambient temperature is in the first temperatureregion, the first control signal whose output value is varied inproportion to the increase of the temperature at the first change rateis output; when the ambient temperature is in the second temperatureregion, the second control signal having the predetermined valueindependent of the temperature is output; when the ambient temperatureis in the third temperature region, the third control signal whoseoutput value is varied in proportion to the temperature at the secondchange rate is output; when the ambient temperature is in the fourthtemperature region, the fourth control signal having the predeterminedvalue independent of the temperature is output; and when the ambienttemperature is in the fifth temperature region, the fifth control signalwhose output value is varied in proportion to the temperature at thethird change rate having the same polarity as the first change rate isoutput. Accordingly, the temperature function having a positive cubiccomponent can be compensated through polygonal lines approximation usingfive straight lines. As a result, even though the number of lines usedin the approximation is five and comparatively small, the approximationcan be sufficiently performed. Therefore, the number of combinations ofadjustment parameters such as proportional coefficients and constants ofthe lines used in the polygonal lines approximation can be decreased,and hence, the adjustment of the respective temperature functions to becompensated can be eased.

Preferably, in the function generator, the analog signal is a voltagesignal, the first and third change rates are negative rates, and thesecond change rate is a positive rate. In this manner, the temperaturefunction having the positive cubic component can be definitelycompensated by the polygonal lines approximation using the five lines.Furthermore, when the voltage signal is used as a control signal for avoltage control crystal oscillating circuit controlled to have anoscillation frequency of a predetermined value through voltage control,a desired oscillation frequency whose dependency on the ambienttemperature is negligible can be definitely obtained.

Preferably, in the function generator, on a graph of the first controlsignal, the second control signal, the third control signal, the fourthcontrol signal and the fifth control signal for representing atemperature characteristic of a quartz oscillator against the ambienttemperature, the first control signal and the fifth control signal arepoint-symmetrical about a coordinate point on the graph determined by atemperature of an inflection point of an oscillation frequency of thequartz oscillator and a value of the third control signal at thetemperature of the inflection point, the second control signal and thefourth control signal are point-symmetrical about the coordinate point,and the third control signal is point-symmetrical about the coordinatepoint. In this manner, the number of the combinations of the adjustmentparameters such as the proportional coefficients and the constants ofthe lines used in the polygonal lines approximation can be furtherdecreased, and hence, the adjustment of the respective temperaturefunctions to be compensated can be further eased.

Preferably, the function generator further comprises storage means,wherein when the ambient temperature is in the first temperature region,the storage means has a first proportion value for defining arelationship between a proportional coefficient between a temperatureused for generating the first control signal and the output valuethereof and a cubic coefficient of a temperature characteristic of anoscillation frequency of a quartz oscillator, and the first proportionvalue is output to the control circuit, when the ambient temperature isin the second temperature region, the storage means has a secondproportion value for defining a relationship between a constant betweena temperature used for generating the second control signal and theoutput value thereof and the cubic coefficient, and the secondproportion value is output to the control circuit, when the ambienttemperature is in the third temperature region, the storage means has athird proportion value for defining a relationship between aproportional coefficient between a temperature used for generating thethird control signal and the output value thereof and the cubiccoefficient, and the third proportion value is output to the controlcircuit, when the ambient temperature is in the fourth temperatureregion, the storage means has a fourth proportion value for defining arelationship between a constant between a temperature used forgenerating the fourth control signal and the output value thereof andthe cubic coefficient, and the fourth proportion value is output to thecontrol circuit, when the ambient temperature is in the fifthtemperature region, the storage means has a fifth proportion value fordefining a relationship between a proportional coefficient between atemperature used for generating the fifth control signal and the outputvalue thereof and the cubic coefficient, and the fifth proportion valueis output to the control circuit, and the storage means stores the firstproportion value, the second proportion value, the third proportionvalue, the fourth proportion value and the fifth proportion value. Inthis manner, in the adjustment of a cubic temperature coefficient of aquartz oscillator, circuit constants corresponding to the proportionalcoefficients of the lines and circuit constants corresponding to theconstants of the lines can be set in a batch. Therefore, fluctuations ofa cubic temperature coefficient and a linear temperature coefficientderived from the AT cut angle of a quartz oscillator and fluctuation ofthe absolute value of the oscillation frequency can be easily anddefinitely adjusted.

Preferably, in the function generator, the control circuit includes afirst NPN transistor whose collector is supplied with a supply voltage,whose base is supplied with a first electric signal decreasing inproportion to the ambient temperature and whose emitter is connectedwith an input of a first current source; a second NPN transistor whosecollector is supplied with the supply voltage, whose base is suppliedwith a second electric signal retaining a predetermined valueindependent of the ambient temperature and whose emitter is connectedwith the input of the first current source; a third NPN transistor whosecollector is supplied with the supply voltage, whose base is suppliedwith a third electric signal increasing inproportion to the ambienttemperature and whose emitter is connected with the input of the firstcurrent source; a fourth NPN transistor whose collector and base areconnected with an output of a second current source having a currentvalue a half as large as a current value of the first current source andwhose emitter is connected with the input of the first current source; afirst PNP transistor whose base is connected with the collector of thefourth NPN transistor, whose emitter is connected with an output of athird current source and whose collector is grounded; a second PNPtransistor whose base is supplied with a fourth electric signalretaining a predetermined value independent of the ambient temperature,whose emitter is connected with the output of the third current sourceand whose collector is grounded; a third PNP transistor whose base issupplied with a fifth electric signal decreasing in proportion to theambient temperature, whose emitter is connected with the output of thethird current source and whose collector is grounded; and a fourth PNPtransistor whose emitter is connected with the output of the thirdcurrent source and whose collector and base are connected with an inputof a fourth current source having a current value a half as large as acurrent value of the third current source, the fourth NPN transistorselects an electric signal having a maximum voltage value among thefirst electric signal, the second electric signal and the third electricsignal and outputs the selected electric signal at the collector thereofas a sixth electric signal, the fourth PNP transistor selects anelectric signal having a minimum voltage value among the fourth electricsignal, the fifth electric signal and the sixth electric signal andoutputs the selected electric signal at the collector thereof as aseventh electric signal, and the control circuit outputs the seventhelectric signal as the control signal. In this manner, the controlsignal can be definitely generated by using the analog signals alone.

Preferably, in the function generator, a first resistance is seriallyconnected between the emitter of the first NPN transistor and the firstcurrent source, a second resistance is serially connected between theemitter of the second NPN transistor and the first current source, athird resistance is serially connected between the emitter of the thirdNPN transistor and the first current source, a fourth resistance isserially connected between the emitter of the fourth NPN transistor andthe first current source, a fifth resistance is serially connectedbetween the emitter of the first PNP transistor and the third currentsource, a sixth resistance is serially connected between the emitter ofthe second PNP transistor and the third current source, a seventhresistance is serially connected between the emitter of the third PNPtransistor and the third current source, and an eighth resistance isserially connected between the emitter of the fourth PNP transistor andthe third current source. In this manner, connecting portions of thecontrol signals in the boundaries between the temperature regions can besmoothed, and hence, even though the polygonal lines approximation isadopted, the approximation error at the connecting portion can be madesmall.

The crystal oscillation device of this invention comprises a firstanalog signal generating circuit for generating and outputting apredetermined analog signal independent of an ambient temperature; asecond analog signal generating circuit for generating and outputting ananalog signal dependent upon the ambient temperature; a control circuitfor receiving the signal from the first analog signal generating circuitand the signal from the second analog signal generating circuit, and forgenerating, with a feasible range of the ambient temperaturecontinuously divided into a first temperature region, a secondtemperature region, a third temperature region, a fourth temperatureregion and a fifth temperature region in this order along a directionfrom a low temperature to a high temperature, control signalsrespectively corresponding to the five temperature regions; and acrystal oscillating circuit for receiving a control signal from thecontrol circuit so as to be controlled to have an oscillation frequencyat a predetermined value by the control signal, wherein the controlcircuit compensates a temperature dependency of the oscillationfrequency output by the crystal oscillating circuit by outputting afirst control signal whose output value is decreased in proportion toincrease of the temperature when the ambient temperature is in the firsttemperature region; a second control signal whose output value iscontinuous with the first control signal and is a predetermined valueindependent of the temperature when the ambient temperature is in thesecond temperature region; a third control signal whose output value iscontinuous with the second control signal and is increased in proportionto increase of the temperature when the ambient temperature is in thethird temperature region; a fourth control signal whose output value iscontinuous with the third control signal and is a predetermined valueindependent of the temperature when the ambient temperature is in thefourth temperature region; and a fifth control signal whose output valueis continuous with the fourth control signal and is decreased inproportion to increase of the temperature when the ambient temperatureis in the fifth temperature region.

The crystal oscillation device of this invention includes the firstanalog signal generating circuit for generating and outputting thepredetermined analog signal independent of the ambient temperature, thesecond analog signal generating circuit for generating and outputtingthe analog signal dependent upon the ambient temperature, and thecontrol circuit for receiving the signal from the first analog signalgenerating circuit and the signal from the second analog signalgenerating circuit and for generating the control signals continuouslycorresponding to the entire regions ranging from the low temperature andthe high temperature. Accordingly, even when the ambient temperature isdivided into the five regions, the frequency skip is not caused in thevicinity of the boundary between the regions, resulting in attaininggood approximation. Moreover, when the ambient temperature is in thefirst temperature region, the first control signal whose output value isdecreased in proportion to the increase of the temperature is output;when the ambient temperature is in the second temperature region, thesecond control signal having the predetermined value independent of thetemperature is output; when the ambient temperature is in the thirdtemperature region, the third control signal whose output value isvaried in proportion to the temperature is output; when the ambienttemperature is in the fourth temperature region, the fourth controlsignal having the predetermined value independent of the temperature isoutput; and when the ambient temperature is in the fifth temperatureregion, the fifth control signal whose output value is decreased inproportion to the increase of the temperature is output. Accordingly,the temperature function having a positive cubic component can becompensated through the polygonal lines approximation using fivestraight lines.

Preferably, in the crystal oscillation device, on a graph of the firstcontrol signal, the second control signal, the third control signal, thefourth control signal and the fifth control signal for representing atemperature characteristic of a quartz oscillator against the ambienttemperature, the first control signal and the fifth control signal arepoint-symmetrical about a coordinate point on the graph determined by atemperature of an inflection point of an oscillation frequency of thequartz oscillator and a value of the third control signal at thetemperature of the inflection point, the second control signal and thefourth control signal are point-symmetrical about the coordinate point,and the third control signal is point-symmetrical about the coordinatepoint. In this manner, the number of the combinations of the adjustmentparameters such as the proportional coefficients and the constants ofthe lines used in the polygonal lines approximation can be furtherdecreased, resulting in further easing the adjustment of the respectivetemperature functions to be compensated.

Preferably, the crystal oscillation device further comprises storagemeans, wherein when the ambient temperature is in the first temperatureregion, the storage means has a first proportion value for defining arelationship between a proportional coefficient between a temperatureused for generating the first control signal and the output valuethereof and a cubic coefficient of a temperature characteristic of anoscillation frequency of a quartz oscillator, and the first proportionvalue is output to the control circuit, when the ambient temperature isin the second temperature region, the storage means has a secondproportion value for defining a relationship between a constant betweena temperature used for generating the second control signal and theoutput value thereof and the cubic coefficient, and the secondproportion value is output to the control circuit, when the ambienttemperature is in the third temperature region, the storage means has athird proportion value for defining a relationship between aproportional coefficient between a temperature used for generating thethird control signal and the output value thereof and the cubiccoefficient, and the third proportion value is output to the controlcircuit, when the ambient temperature is in the fourth temperatureregion, the storage means has a fourth proportion value for defining arelationship between a constant between a temperature used forgenerating the fourth control signal and the output value thereof andthe cubic coefficient, and the fourth proportion value is output to thecontrol circuit, when the ambient temperature is in the fifthtemperature region, the storage means has a fifth proportion value fordefining a relationship between a proportional coefficient between atemperature used for generating the fifth control signal and the outputvalue thereof and the cubic coefficient, and the fifth proportion valueis output to the control circuit, and the storage means stores the firstproportion value, the second proportion value, the third proportionvalue, the fourth proportion value and the fifth proportion value. Inthis manner, in the adjustment of a cubic temperature coefficient of aquartz oscillator, circuit constants corresponding to the proportionalcoefficients of the lines and circuit constants corresponding to theconstants of the lines can be set in a batch. As a result, fluctuationsof a cubic temperature coefficient and a linear temperature coefficientderived from the AT cut angle of a quartz oscillator and fluctuation ofthe absolute value of the oscillation frequency can be easily anddefinitely adjusted.

Preferably, in the crystal oscillation device, the control circuitincludes a first NPN transistor whose collector is supplied with asupply voltage, whose base is supplied with a first electric signaldecreasing in proportion to the ambient temperature and whose emitter isconnected with an input of a first current source; a second NPNtransistor whose collector is supplied with the supply voltage, whosebase is supplied with a second electric signal retaining a predeterminedvalue independent of the ambient temperature and whose emitter isconnected with the input of the first current source; a third NPNtransistor whose collector is supplied with the supply voltage, whosebase is supplied with a third electric signal increasing in proportionto the ambient temperature and whose emitter is connected with the inputof the first current source; a fourth NPN transistor whose collector andbase are connected with an output of a second current source having acurrent value a half as large as a current value of the first currentsource and whose emitter is connected with the input of the firstcurrent source; a first PNP transistor whose base is connected with thecollector of the fourth NPN transistor, whose emitter is connected withan output of a third current source and whose collector is grounded; asecond PNP transistor whose base is supplied with a fourth electricsignal retaining a predetermined value independent of the ambienttemperature, whose emitter is connected with the output of the thirdcurrent source and whose collector is grounded; a third PNP transistorwhose base is supplied with a fifth electric signal decreasing inproportion to the ambient temperature, whose emitter is connected withthe output of the third current source and whose collector is grounded;and a fourth PNP transistor whose emitter is connected with the outputof the third current source and whose collector and base are connectedwith an input of a fourth current source having a current value a halfas large as a current value of the third current source, the fourth NPNtransistor selects an electric signal having a maximum voltage valueamong the first electric signal, the second electric signal and thethird electric signal and outputs the selected electric signal at thecollector thereof as a sixth electric signal, the fourth PNP transistorselects an electric signal having a minimum voltage value among thefourth electric signal, the fifth electric signal and the sixth electricsignal and outputs the selected electric signal at the collector thereofas a seventh electric signal, and the control circuit outputs theseventh electric signal as the control signal. In this manner, thecontrol signal can be definitely generated by using the analog signalsalone.

Preferably, in the crystal oscillation device, a first resistance isserially connected between the emitter of the first NPN transistor andthe first current source, a second resistance is serially connectedbetween the emitter of the second NPN transistor and the first currentsource, a third resistance is serially connected between the emitter ofthe third NPN transistor and the first current source, a fourthresistance is serially connected between the emitter of the fourth NPNtransistor and the first current source, a fifth resistance is seriallyconnected between the emitter of the first PNP transistor and the thirdcurrent source, a sixth resistance is serially connected between theemitter of the second PNP transistor and the third current source, aseventh resistance is serially connected between the emitter of thethird PNP transistor and the third current source, and an eighthresistance is serially connected between the emitter of the fourth PNPtransistor and the third current source. In this manner, connectingportions of the control signals in the boundaries between thetemperature regions can be smoothed, and hence, even though thepolygonal lines approximation is adopted, the approximation error at theconnection portion can be made small.

Preferably, the crystal oscillation device further comprises a RAMcircuit for storing parameters, for compensating the temperaturedependency of the oscillation frequency of the crystal oscillatingcircuit, of the first through fifth control signals output by thecontrol circuit, with varying each of the parameters with regard to eachof the control signals; and a programmable ROM circuit for storingoptimal parameters of the parameters with regard to each of the controlsignals. In this manner, the control signals can be adjusted withappropriately varying externally input data of the RAM circuit on eachof the control signals and an optimal control signal characteristic canbe detected. In addition, the detected optimal data can be read, afterwriting them in a PROM circuit, under actual use conditions, so as toconfirm that a control signal in accordance with the ambient temperaturecan be definitely output.

Preferably, the crystal oscillation device further comprises optimizingmeans for optimizing the control signals output by the control circuitindependently of one another and in accordance with a cubic temperaturecoefficient, a linear temperature coefficient, a frequency differencefrom a reference frequency at a temperature of an inflection point andthe temperature of the inflection point of the temperature dependency ofthe oscillation frequency of the crystal oscillating circuit. In thismanner, the temperature dependency of the oscillation frequency of eachquartz oscillator can be definitely coped with, resulting in improvingthe approximation characteristic of the temperature compensation.

The method of this invention of adjusting a crystal oscillation deviceis adopted in a crystal oscillation device including a first analogsignal generating circuit for generating and outputting a predeterminedanalog signal independent of an ambient temperature; a second analogsignal generating circuit for generating and outputting an analog signaldependent upon the ambient temperature; a control circuit for receivingthe signal from the first analog signal generating circuit and thesignal from the second analog signal generating circuit, and forgenerating, with a feasible range of the ambient temperaturecontinuously divided into a first temperature region, a secondtemperature region, a third temperature region, a fourth temperatureregion and a fifth temperature region in this order along a directionfrom a low temperature to a high temperature, control signalsrespectively corresponding to the five temperature regions; a crystaloscillating circuit for receiving a control signal from the controlcircuit so as to be controlled to have an oscillation frequency at apredetermined value by the control signal; a RAM circuit for storingparameters, for compensating a temperature dependency of the oscillationfrequency of the crystal oscillating circuit, of the first through fifthcontrol signals output by the control circuit, with varying each of theparameters with regard to each of the control signals; and aprogrammable ROM circuit for storing optimal parameters of theparameters with regard to each of the control signals, the controlcircuit outputting a first control signal whose output value isdecreased in proportion to increase of the temperature when the ambienttemperature is in the first temperature region; a second control signalwhose output value is continuous with the first control signal and is apredetermined value independent of the temperature when the ambienttemperature is in the second temperature region; a third control signalwhose output value is continuous with the second control signal and isincreased in proportion to increase of the temperature when the ambienttemperature is in the third temperature region; a fourth control signalwhose output value is continuous with the third control signal and is apredetermined value independent of the temperature when the ambienttemperature is in the fourth temperature region; and a fifth controlsignal whose output value is continuous with the fourth control signaland is decreased in proportion to increase of the temperature when theambient temperature is in the fifth temperature region, and the methodcomprises a peculiar parameter determining step of determining peculiarparameters by allowing the crystal oscillation device to stand at atemperature continuously varying from the first temperature region tothe fifth temperature region and by calculating parameters of thecontrol signals respectively corresponding to a cubic temperaturecoefficient, a linear temperature coefficient, a frequency differencefrom a reference frequency at a temperature of an inflection point andthe temperature of the inflection point of the temperaturecharacteristic of the crystal oscillating circuit so as to makevariation of the oscillation frequency output by the crystal oscillatingcircuit caused by the temperature substantially zero; an initialparameter determining step of determining initial parameters bymeasuring an initial temperature characteristic of the control signalsoutput by the control circuit and by calculating the parameters of thecontrol signals respectively corresponding to the cubic temperaturecoefficient, the linear temperature coefficient, the frequencydifference from the reference frequency at the temperature of theinflection point and the temperature of the inflection point; and anoptimal parameter writing step of obtaining change amounts of thecontrol signals per unit of data corresponding to temperaturecompensating parameters stored in the RAM circuit by measuring a changeamount of the initial temperature characteristic with changing the datacorresponding to the temperature compensating parameters, obtainingdifferences between the initial parameters and the peculiar parameters,determining optimal parameters of the control signals so as to minimizethe differences on the basis of the change amounts of the controlsignals per unit of the data, and writing the optimal parameters in theROM circuit.

According to the method of this invention of adjusting a crystaloscillation device, each peculiar parameter of the control signal isdetermined, by allowing the crystal oscillation device to stand at atemperature continuously changing from the first temperature region tothe fifth temperature region, so that the variation of the oscillationfrequency output by the crystal oscillating circuit caused by the changeof the temperature can be substantially zero. After determining eachinitial parameter of the control signal, by measuring the change amountof the initial temperature characteristic with changing datacorresponding to the temperature compensating parameter stored in theRAM circuit, the change amount of the control signal per unit of thedata corresponding to the temperature compensating parameter isobtained. After obtaining the difference between the initial parameterand the peculiar parameter, the optimal parameter of the control signalis determined on the basis of the change amount of the control signalper unit of the data so as to make the difference small. Accordingly,the fluctuation of the AT cut angle of a quartz oscillator, offsetfluctuation of the oscillation frequency, and the fluctuation of thetemperature of an inflection point can be easily and definitely adjustedwith regard to each crystal oscillation device. Moreover, since theambient temperature is divided into five regions and polygonal linesapproximation using five lines is adopted, the number of the temperaturecharacteristic compensating parameters can be small. As a result, thecircuit scale of the RAM circuit and the ROM circuit can be made small,and hence, the entire device can easily attain compactness.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a functional block diagram for showing a temperaturecompensating crystal oscillation device according to a first embodimentof the invention;

FIG. 2 is a circuit diagram of a voltage control crystal oscillatingcircuit of the temperature compensating crystal oscillation device ofthe first embodiment;

FIG. 3 is a circuit diagram of a constant voltage circuit and atemperature sensor circuit of the temperature compensating crystaloscillation device of the first embodiment;

FIG. 4 is a detailed circuit diagram of the constant voltage circuit ofthe temperature compensating crystal oscillation device of the firstembodiment;

FIG. 5 is a detailed circuit diagram of the temperature sensor circuitof the temperature compensating crystal oscillation device of the firstembodiment;

FIG. 6 is another circuit diagram of the constant voltage circuit andthe temperature sensor circuit of the temperature compensating crystaloscillation device of the first embodiment;

FIG. 7 is another detailed circuit diagram of the constant voltagecircuit of the temperature compensating crystal oscillation device ofthe first embodiment;

FIG. 8 is another detailed circuit diagram of the temperature sensorcircuit of the temperature compensating crystal oscillation device ofthe first embodiment;

FIG. 9 is another detailed circuit diagram of the temperature sensorcircuit of the temperature compensating crystal oscillation device ofthe first embodiment;

FIG. 10 is a detailed circuit diagram of a control circuit of thetemperature compensating crystal oscillation device of the firstembodiment;

FIGS. 11(a) through 11(c) show compensation of an oscillation frequencyof the voltage control crystal oscillating circuit using a controlvoltage in the temperature compensating crystal oscillation device ofthe first embodiment, wherein FIG. 11(a) is a graph for showing theambient temperature dependency of the oscillation frequency beforetemperature compensation, FIG. 11(b) is a graph for showing the ambienttemperature dependency of the control voltage used for the temperaturecompensation output by the control circuit and FIG. 11(c) is a graph forshowing the ambient temperature dependency of a difference between theoscillation frequency and a reference frequency attained by applying thecontrol voltage to the voltage control crystal oscillating circuit;

FIG. 12 is a graph for showing the ambient temperature dependency of thecontrol voltage to be used for the temperature compensation usingpolygonal lines approximation in the temperature compensating crystaloscillation device of the first embodiment;

FIG. 13 is a detailed circuit diagram of a ROM/RAM circuit of thetemperature compensating crystal oscillation device of the firstembodiment;

FIG. 14 is a timing chart of RAM data input to the ROM/RAM circuit ofthe temperature compensating crystal oscillation device of the firstembodiment;

FIG. 15 is a detailed circuit diagram of a control circuit of atemperature compensating crystal oscillation device according to a firstmodification of the first embodiment;

FIGS. 16(a) through 16(c) show compensation of an oscillation frequencyof a voltage control crystal oscillating circuit using a control voltagein a temperature compensating crystal oscillation device according to asecond modification of the first embodiment, wherein FIG. 16(a) is agraph for showing the ambient temperature dependency of the oscillationfrequency before temperature compensation, FIG. 16(b) is a graph forshowing the ambient temperature dependency of the control voltage to beused for the temperature compensation output by a control circuit andFIG. 16(c) is a graph for showing the ambient temperature dependency ofa difference between the oscillation frequency and a reference frequencyattained by applying the control voltage to the voltage control crystaloscillating circuit;

FIGS. 17(a) through 17(c) show compensation of an oscillation frequencyof a voltage control crystal oscillating circuit using a control voltagein a temperature compensating crystal oscillation device according to athird modification of the first embodiment, wherein FIG. 17(a) is agraph for showing the ambient temperature dependency of the oscillationfrequency before temperature compensation, FIG. 17(b) is a graph forshowing the ambient temperature dependency of the control voltage usedfor the temperature compensation output by a control circuit and FIG.17(c) is a graph for showing the ambient temperature dependency of adifference between the oscillation frequency and a reference frequencyattained by applying the control voltage to the voltage control crystaloscillating circuit;

FIG. 18 is a table for showing comparison in a memory capacity attainedby various control circuit systems of the control circuit in thetemperature compensating crystal oscillation device of the firstembodiment;

FIG. 19(a) is a graph for showing the ambient temperature dependencyattained by different cubic temperature coefficients of the oscillationfrequency before the temperature compensation and FIG. 19(b) is a graphfor showing the ambient temperature dependency of a control voltageoutput by a control circuit of a crystal oscillation device according toa fourth modification of the first embodiment;

FIGS. 20(a) through 20(c) are graphs for showing generation of thecontrol voltage output by the control circuit of the crystal oscillationdevice of the fourth modification of the first embodiment;

FIG. 21(a) is a graph for showing the respective ambient temperaturedependencies of the control voltage output by the control circuit of thecrystal oscillation device of the fourth modification of the firstembodiment and an ideal control voltage peculiar to a quartz oscillatorand FIG. 21(b) is a graph for showing a difference between the idealcontrol voltage and an approximation control voltage;

FIG. 22 is a functional block diagram of a functional generator used fortemperature compensation in a temperature compensating crystaloscillation device according to a second embodiment of the invention;

FIGS. 23(a) through 23(d) are graphs for explaining variation of acontrol voltage through adjustment of temperature compensatingparameters and a inflection point temperature in the temperaturecompensating crystal oscillation device of the second embodiment;

FIG. 24 is a functional block diagram for illustrating adjustment of anoscillation frequency in a temperature compensating crystal oscillationdevice according to a third embodiment of the invention;

FIG. 25 is a flowchart for showing the adjustment of the temperaturecompensating crystal oscillation device of the third embodiment;

FIGS. 26(a) through 26(c) are graphs for illustrating adjustment of anideal temperature compensating crystal oscillation device, wherein FIG.26(a) is a graph for showing the ambient temperature dependency of anoscillation frequency before temperature compensation, FIG. 26(b) is agraph for showing the ambient temperature dependency of a controlvoltage used for the temperature compensation and FIG. 26(c) is a graphfor showing the ambient temperature dependency of a difference betweenthe oscillation frequency and a reference frequency after thetemperature compensation;

FIG. 27 is a functional block diagram of a conventional temperaturecompensating crystal oscillation device; and

FIGS. 28(a) through 28(c) are graphs for explaining temperaturecompensation of the conventional temperature compensating crystaloscillation device.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

A first embodiment of the invention will now be described with referenceto the accompanying drawings.

FIG. 1 is a functional block diagram of a temperature compensatingcrystal oscillation device of the first embodiment. The temperaturecompensating crystal oscillation device (TCXO) 10 shown in FIG. 1 is,for example, an oscillation device for generating a reference clocksignal in a portable telephone, and is required to have stable frequencyaccuracy such that variation of the oscillation frequency can be withina range of ±2.5 ppm or less in the entire temperature range.

As is shown in FIG. 1, the temperature compensating crystal oscillationdevice 10 includes a constant voltage circuit 12 serving as a firstanalog signal generating circuit for generating and outputting apredetermined voltage independent of the ambient temperature; atemperature sensor circuit 13 serving as a second analog signalgenerating circuit for generating and outputting a voltage varied inproportion to the ambient temperature; a third analog signal generatingcircuit 17 for receiving the constant voltage output by the constantvoltage circuit 12 and the voltage in proportion to the temperatureoutput by the temperature sensor circuit 13 and for outputting a voltagewhich corresponds to a given temperature within each of five temperatureregions obtained by dividing the entire range of a feasible ambienttemperature into five parts; and a control circuit 14 for receiving thevoltage outputted from the third analog signal generating circuit 17 andfor generating a control voltage Vc used for polygonal linesapproximation of a negative cubic curve by using continuous straightlines for compensating the temperature characteristic of a quartzoscillator in the entire range of the ambient temperature; a voltagecontrol crystal oscillating circuit (hereinafter referred to as theVCXO) 15 whose oscillation frequency is controlled to be a predeterminedvalue by the control voltage Vc received from the control circuit 14;and a ROM/RAM circuit 16 for storing temperature compensating parametersfor compensating the temperature characteristic of the control voltageVc for optimizing the oscillation frequency output by the VCXO 15 inaccordance with the control voltage Vc output by the control circuit 14.

In this case, the ambient temperature may be the temperature of VCXO 15or may be the temperature of the crystal oscillation device 10.

FIG. 2 is an exemplified circuit diagram of the VCXO 15 of thisembodiment and shows a known circuit configuration. As is shown in FIG.2, an input terminal 21 for receiving the control voltage Vc isconnected with one terminal of a quartz oscillator 23 with a biasresistance 22 interposed therebetween. Between the bias resistance 22and the quartz oscillator 23 is connected the cathode terminal of avaractor diode 24 with its anode terminal grounded. The oscillationfrequency of the quartz oscillator 23 is changed by varying thecapacitance of the varactor diode 24 by changing the control voltage Vc.The other terminal of the quartz oscillator 23 is connected with aColpitts crystal oscillating circuit 25, and the oscillation output foutof the Colpitts crystal oscillating circuit 25 is output to an outputterminal 26.

Now, the constant voltage circuit 12 and the temperature sensor circuit13 of this embodiment are described in detail with reference to theaccompanying drawings.

FIG. 3 is a circuit diagram for showing the configuration of a monotonedecrease voltage generating circuit 30, including the constant voltagecircuit 12 and the temperature sensor circuit 13 of FIG. 1, forgenerating and outputting a first control voltage y₁ or a fifth controlvoltage y₅ which decreases in proportion to increase of the ambienttemperature T_(a). As is shown in FIG. 3, the monotone decrease voltagegenerating circuit 30 includes a constant voltage circuit 31, and abandgap reference circuit 32 and a current mirror circuit 33 working asthe temperature sensor circuit. A reference voltage V0 of approximately1.25 V independent of the ambient temperature T_(a) is generated in thebandgap reference circuit 32, and a constant current I₀ is generated onthe basis of the reference voltage V0 in the constant voltage circuit31.

Also, a current I_(T0) dependent upon the ambient temperature T_(a) isgenerated in the bandgap reference circuit 32, and a current I_(T) inproportion to the ambient temperature T_(a) is generated in the currentmirror circuit 33, so that a difference current I₀−I_(T) between theconstant current I₀ and the current I_(T) in proportion to the ambienttemperature T_(a) can be taken out at a node between the constantvoltage circuit 31 and the current mirror circuit 33. The differencecurrent I₀−I_(T) is subjected to current/voltage conversion by using aresistance 34, thereby generating the first control voltage y₁ or thefifth control voltage y₅ which decreases in accordance with the increaseof the ambient temperature T_(a). At this point, the absolute value ofthe first control voltage y₁ or the fifth control voltage y₅ is set byadjusting a resistance value of a resistance 31 a supplied with a supplyvoltage Vcc in the constant voltage circuit 31.

FIG. 4 is a circuit diagram for showing another configuration of theconstant voltage circuit 31 shown in FIG. 3. As is shown in FIG. 4, theconstant voltage circuit 31 includes an operational amplifier 311supplied, at its positive terminal, with the reference voltage V0independent of the ambient temperature T_(a) output by the bandgapreference circuit 32; an NPN transistor 312 whose base is supplied withthe output of the operational amplifier 311 and whose emitter isconnected with a negative terminal of the operational amplifier 311 andthe resistance 31 a; a PNP transistor 313 whose collector is connectedwith the collector of the NPN transistor 312; and the resistance 31 aconnected with the emitter of the NPN transistor 312 at its one end andgrounded at the other end. A current I₀₀ flowing from PNP transistors315 through PNP transistors 316 flows into the resistance 31 a, so as togenerate the reference voltage V0 independent of the ambient temperatureT_(a), namely, a voltage Vbc at the base of the PNP transistor 313 makesa contribution to the generation of the constant current I₀ independentof the ambient temperature T_(a).

Also, the constant voltage circuit 31 is connected with the ROM/RAMcircuit 16 of FIG. 1, so that plural temperature compensating parameterscan be adjusted. For example, in order to copewith change of a 5-bitsignal Ti for defining an inflection point temperature input from theROM/RAM circuit 16, the constant voltage circuit 31 includes five PNPtransistors 315 supplied with the base voltage Vbc at their shared base,five PNP transistors 316 for feeding back a current to the emitter ofthe NPN transistor 312 and five switching NPN transistors 317 each ofwhich is closed/opened in accordance with each bit of the 5-bit signalTi.

FIG. 5 shows another circuit configuration of the bandgap referencecircuit 32 and the current mirror circuit 33 shown in FIG. 3. As isshown in FIG. 5, the bandgap reference circuit 32 includes a pair of PNPtransistors 321 and 322 connected with each other at their bases; fourNPN transistors 323, 324, 325 and 326 connected in parallel with thecollector and the base of the PNP transistor 321 and connected with eachother at their bases; an NPN transistor 328 sharing the base with theNPN transistors 323, 324, 325 and 326 and connected with the collectorof the PNP transistor 322 through a resistance 327; and a resistance 329connected with the emitter shared by the four NPN transistors 323, 324,325 and 326 at its one end and grounded at the other end. The basevoltage Vbt of the pair of PNP transistors 321 and 322 is a voltage usedfor transferring a current increasing in proportion to the ambienttemperature T_(a).

Furthermore, the current mirror circuit 33 of FIG. 5 is connected withthe ROM/RAM circuit 16 of FIG. 1, so that the temperature compensatingparameters can be adjusted. For example, in order to cope with change ofa 4-bit signal b₁ corresponding to the constant term of the firstcontrol voltage y₁ or a 4-bit signal b₅ corresponding to the constantterm of the fifth control voltage y₅ input from the ROM/RAM circuit 16,the current mirror circuit 33 includes four PNP transistors 331 suppliedwith the base voltage Vbc from the constant voltage circuit 31 at theirshared base, four PNP transistors 332 for transferring the constantcurrent I₀, and four switching NPN transistors 333 respectivelyconnected in parallel with the four PNP transistors 332 andclosed/opened in accordance with the 4-bit signal b₁ or b₅. Furthermore,the current mirror circuit 33 includes four PNP transistors 334supplied, at their shared base, with the base voltage Vbt dependent uponthe temperature supplied from the bandgap reference circuit 32; eightNPN transistors 335 constituting four current mirror circuitsrespectively connected in parallel with the four PNP transistors 334 forabsorbing a current through mirror inversion; and four switching NPNtransistors 336 connected in parallel with the four groups of NPNtransistors 335 and closed/opened in accordance with a 4-bit signal a₁corresponding to the proportional coefficient of the first controlvoltage y₁ or a 4-bit signal a₅ corresponding to the proportionalcoefficient of the fifth control voltage y₅. When, among the fourswitching NPN transistors 333, the number of transistors in an on-stateis changed in accordance with the 4-bit signal b₁ or b₅, the constantcurrent I₀ is increased/decreased, and when, among the four switchingNPN transistors 336, the number of transistors in an on-state is changedin accordance with the 4-bit signal a₁ or a₅, the current I_(T)dependent upon the temperature is increased/decreased. As a result, theoutput current I₀−I_(T) for determining the first control voltage y₁ orthe fifth control voltage y₅ is increased/decreased.

FIG. 6 shows the detailed circuit configuration of a monotone increasevoltage generating circuit 40, including the constant voltage circuit 12and the temperature sensor circuit 13 of FIG. 1, for generating andoutputting a third control voltage y₃ which increases in accordance withthe increase of the ambient temperature T_(a). As is shown in FIG. 6,the monotone increase voltage generating circuit 40 includes a constantvoltage circuit 41, and a bandgap reference circuit 42 and a currentmirror circuit 43 serving as the temperature sensor circuit. A referencevoltage V0 of approximately 1.25 V independent of the ambienttemperature T_(a) is generated in the bandgap reference circuit 42, anda constant current I₀ is generated on the basis of the reference voltageV0 in the constant voltage circuit 41.

Also, a current I_(T0) dependent upon the ambient temperature T_(a) isgenerated in the bandgap reference circuit 42, and a current I_(T) inproportion to the ambient temperature T_(a) is generated in the currentmirror circuit 43, so that a difference current I_(T)−I₀ between thecurrent I_(T) in proportion to the ambient temperature T_(a) and theconstant current I₀ can be taken out at a node between the constantvoltage circuit 41 and the current mirror circuit 43. The differencecurrent I_(T)−I₀ is subjected to the current/voltage conversion by usinga resistance 44, thereby generating the third control voltage y₃ inproportion to the ambient temperature T_(a). At this point, a differenceat room temperature between the third control voltage y₃ and a voltagefor attaining a reference frequency at the inflection point temperatureis set by adjusting the resistance value of a resistance 41 a of theconstant voltage circuit 41.

FIG. 7 shows the detailed circuit configuration of the constant voltagecircuit 41. In FIG. 7, like reference numerals are used to refer to likeelements shown in FIG. 4 and the description is omitted. In this case,it goes without saying that the constant voltage circuit 41 has adifferent circuit constant from the constant voltage circuit 31.

FIG. 8 shows the detailed circuit configuration of the bandgap referencecircuit 42 and the current mirror circuit 43. The bandgap referencecircuit 42 of FIG. 8 has the same configuration as the bandgap referencecircuit 32 of FIG. 5, and hence, the description is omitted with likereference numerals used to refer to like elements shown in FIG. 5. InFIG. 8, the current mirror circuit 43 is connected with the ROM/RAMcircuit 16 of FIG. 1, so that the temperature compensating parameterscan be adjusted. For example, in order to cope with change of a 4-bitsignal a₃ corresponding to the proportional coefficient of the thirdcontrol voltage y₃ input from the ROM/RAM circuit 16, the current mirrorcircuit 43 includes four PNP transistors 431 supplied, at their sharedbase, with the base voltage Vbt dependent upon the temperature inputfrom the band gap reference circuit 42, four PNP transistors 432 fortransferring the current I_(T) in proportion to the ambient temperatureT_(a), and four switching NPN transistors 433 respectively connected inparallel with the four PNP transistors 432 and closed/opened inaccordance with the 4-bit signal a₃. Moreover, the current mirrorcircuit 43 includes four PNP transistors 434 supplied, at their sharedbase, with the base voltage Vbc input from the constant voltage circuit41, eight NPN transistors 435 constituting four current mirror circuitsrespectively connected in parallel with the four PNP transistors 434 forabsorbing the current through the mirror inversion, and four switchingNPN transistors 436 respectively connected in parallel with the fourgroups of NPN transistors 435 and closed/opened in accordance with the4-bit signal a₃. When, the number of transistors in an on-state amongthe four switching NPN transistors 433 and the number of transistors inan on-state among the four switching NPN transistors 436 are changed inaccordance with the 4-bit signal a₃, the output current I_(T)−I₀ fordetermining the third control voltage y₃ is increased/decreased.

FIG. 9 shows a part of the circuit configuration of a constant voltagegenerating circuit, including the constant voltage circuit 12 and thetemperature sensor circuit 13 of FIG. 1, for generating and outputting asecond control voltage y₂ and a fourth control voltage y₄ independent ofthe ambient temperature. This constant voltage generating circuitincludes a constant voltage circuit (not shown) and a bandgap referencecircuit 42A and a current mirror circuit 43A serving as the temperaturesensor circuit. The constant voltage circuit has a configurationequivalent to the constant voltage circuit 41 of FIG. 7. The bandgapreference circuit 42A of FIG. 9 has the same configuration as thebandgap reference circuit 42 of FIG. 8, and hence, the description isomitted with like reference numerals used to refer to like elementsshown in FIG. 8.

Also, the current mirror circuit 43A of FIG. 9 is connected with theROM/RAM circuit 16 of FIG. 1, so that the temperature compensatingparameters can be adjusted. For example, in order to cope with change ofa 4-bit signal b₄ corresponding to the constant term of the fourthcontrol voltage y₄ input from the ROM/RAM circuit 16, the current mirrorcircuit 43A includes four PNP transistors 431 supplied, at their sharedbase, with the base voltage Vbc input from the constant voltage circuit,four PNP transistors 432 for transferring the constant current I₀, andfour switching NPN transistors 433 respectively connected in parallelwith the PNP transistors 432 and closed/opened in accordance with the4-bit signal b₄. The current mirror circuit 43A further includes fourPNP transistors 434 supplied, at their shared base, with the basevoltage Vbc input from the constant voltage circuit, eight NPNtransistors 435 constituting four current mirror circuits respectivelyconnected in parallel with the four PNP transistors 434 for absorbingthe current through the mirror inversion, and four switching NPNtransistors 436 respectively connected in parallel with the four groupsof NPN transistors 435 and closed/opened in accordance with a 4-bitsignal b₂. When the number of transistors in an on-state among the fourswitching NPN transistors 433 is changed in accordance with the 4-bitsignal b₄, the current for determining the fourth control voltage y₄ isincreased/decreased, and when the number of transistors in an on-stateamong the four switching NPN transistors 436 is changed in accordancewith the 4-bit signal b₂, the current for determining the second controlvoltage y₂ is increased/decreased.

Next, the control circuit 14 of this embodiment will be described withreference to the accompanying drawings.

FIG. 10 shows the detailed circuit configuration of the control circuit14 of FIG. 1. As is shown in FIG. 10, the control circuit 14 forgenerating the control voltage Vc used for the temperature compensationof the VCXO 15 includes a MAX circuit 14 a for receiving the firstcontrol voltage y₁, the second control voltage y₂ and the third controlvoltage y₃ generated by the constant voltage circuit 12 and thetemperature sensor circuit 13 of FIG. 1 and for outputting the maximumvoltage among these control voltages as a sixth control voltage y₆; anda MIN circuit 14 b for receiving the fourth control voltage y₄ and thefifth control voltage y₅ generated by the constant voltage circuit 12and the temperature sensor circuit 13 of FIG. 1 and the sixth controlvoltage y₆ output by the MAX circuit 14 a and for outputting the minimumvoltage among these control voltages as a seventh control voltage y₇.The seventh control voltage y₇ works as the control voltage Vc for thetemperature compensation.

The MAX circuit 14 a includes a first NPN transistor Q1 whose collectoris supplied with a supply voltage Vcc, whose base is supplied with thefirst control voltage y₁ and whose emitter is connected with the inputof a first constant current source I₁; a second NPN transistor Q2 whosecollector is supplied with the supply voltage Vcc, whose base issupplied with the second control voltage y₂ and whose emitter isconnected with the input of the first constant current source I₁; athird NPN transistor Q3 whose collector is supplied with the supplyvoltage Vcc, whose base is supplied with the third control voltage y₃and whose emitter is connected with the input of the first constantcurrent source I₁; and a fourth NPN transistor Q7 whose collector andbase are connected with the output of a second constant current sourceI₂ for supplying a current with a value a half as large as that of thefirst constant current source I₁ and whose emitter is connected with theinput of the first constant current source I₁, for outputting, at itscollector, the maximum voltage among the first control voltage y₁, thesecond control voltage y₂ and the third control voltage y₃ as the sixthcontrol voltage y₆.

The MIN circuit 14 b includes a first PNP transistor Q6 whose base isconnected with the collector of the fourth NPN transistor Q7, whoseemitter is connected with the output of a third constant current sourceI₃ and whose collector is grounded; a second PNP transistor Q4 whosebase is supplied with the fourth control voltage y₄, whose emitter isconnected with the output of the third constant current source I₃ andwhose collector is grounded; a third PNP transistor Q5 whose base issupplied with the fifth control voltage y₅, whose emitter is connectedwith the output of the third constant current source I₃ and whosecollector is grounded; and a fourth PNP transistor Q8 whose emitter isconnected with the output of the third constant current source I₃ andwhose collector and base are connected with the input of a fourthconstant current source I₄ for supplying a current with a value a halfas large as that of the third constant current source I₃, foroutputting, at its collector, the minimum voltage among the fourthcontrol voltage y₄, the fifth control voltage y₅ and the sixth controlvoltage y₆ as the seventh control voltage y₇.

The MAX circuit 14 a and the MIN circuit 14 b having the aforementionedconfigurations are operated as follows:

In the MAX circuit 14 a, the first NPN transistor Q1, the second NPNtransistor Q2 and the third NPN transistor Q3 mutually share thecollector and the emitter, the current from the second constant currentsource I₂ flows through the fourth NPN transistor Q7 to the firstconstant current source I₁ and the current value I₂ is set at I₁/2.Therefore, the remaining current value I₁/2 of the current value I₁flows to one transistor supplied with the largest voltage at the basethereof among the first NPN transistor Q1, the second NPN transistor Q2and the third NPN transistor Q3. As a result, a potential differencebetween the base and the emitter of the fourth NPN transistor Q7 isequal to a potential difference between the base and the emitter of thatone transistor supplied with the largest voltage among the first NPNtransistor Q1, the second NPN transistor Q2 and the third NPN transistorQ3. Accordingly, a voltage shared by the collector and the base of thefourth NPN transistor Q7 is equal to the maximum voltage among the firstcontrol voltage y₁, the second control voltage y₂ and the third controlvoltage y₃.

Also, in the MIN circuit 14 b, the first PNP transistor Q6, the secondPNP transistor Q4 and the third PNP transistor Q5 mutually share theemitter, and the collectors of these transistors are all grounded.Therefore, a voltage shared by the collector and the base of the fourthPNP transistor Q8 is equal to the minimum voltage among those suppliedto the first PNP transistor Q6, the second PNP transistor Q4 and thethird PNP transistor Q5.

In this manner, according to the control circuit 14 of this embodimentfor generating the control voltage Vc for the temperature compensationof the VCXO 15, the polygonal lines approximation of the temperaturecompensation characteristic can be performed by outputting a group offive continuously and linearly changing control voltages as the seventhcontrol voltage y₇ corresponding to the control voltage Vc by usingplural simple bipolar circuits.

Furthermore, since all of the constant voltage circuit 12, thetemperature sensor circuit 13 and the control circuit 14 togetherworking as a function generator for generating the control voltage Vcfor the temperature compensation include analog circuits alone, there isno possibility of occurrence of a quantum noise in principle, and hence,frequency skip can be prevented from occurring at the connecting portionbetween polygonal lines. In addition, since there is no need to providethe function generator with a clock generator, a clock noise can also beavoided.

Although the output of the MAX circuit 14 a is received by the MINcircuit 14 b in FIG. 10, the order of the connection of the MAX circuit14 a and the MIN circuit 14 b can be reversed. Specifically, in thatcase, the third control voltage y₃, the fourth control voltage y₄ andthe fifth control voltage y₅ are input to the MIN circuit 14 b, whoseoutput is used as the sixth control voltage y₆. The sixth controlvoltage y₆, the first control voltage y₁ and the second control voltagey₂ are input to the MAX circuit 14 a, whose output is used as theseventh control voltage y₇, namely, the output of the control circuit14.

Now, the control voltage Vc used for the temperature compensationgenerated by the constant voltage circuit 12, the temperature sensorcircuit 13 and the control circuit 14 of FIG. 1 together working as thefunction generator will be described by using graphs and formulas.

FIGS. 11(a) through 11(c) show the compensation of the oscillationfrequency f of the VCXO 15 using the temperature compensating controlvoltage Vc, and FIG. 11(a) shows the dependency on the ambienttemperature T_(a) of the oscillation frequency f output by the VCXO 15without the temperature compensation, wherein f₀ indicates a referencefrequency determined by a specification of, for example, a portabletelephone. FIG. 11(b) shows the dependency on the ambient temperatureT_(a) of the control voltage Vc (i.e., the seventh control voltage y₇)for the temperature compensation output by the control circuit 14, andFIG. 11(c) shows the temperature dependency of a difference Δf betweenthe oscillation frequency f of the VCXO 15 and the reference frequencyf₀ attained by applying the control voltage Vc to the VCXO 15.

FIG. 12 shows the details of the graph of FIG. 11(b), and shows a groupof polygonal lines respectively corresponding to the first controlvoltage y₁ in a first temperature region (T₀≦T_(a)<T₁), the secondcontrol voltage y₂ in a second temperature region (T₁≦T_(a)<T₂), thethird control voltage y₃ in a third temperature region (T₂≦T_(a)<T₃),the fourth control voltage y₄ in a fourth temperature region(T₃≦T_(a)<T₄), and the fifth control voltage y₅ in a fifth temperatureregion (T₄≦T_(a)<T₅). As is shown in FIG. 12, the X-axis indicates theambient temperature T_(a), the Y-axis indicates the control voltage Vc,a center temperature of the control voltage Vc is indicated as T_(i),and a voltage difference from a voltage for attaining the referencefrequency at the center temperature T_(i) is indicated as γ.

The linear functional formulas of y₁ through y₅ are:

y ₁ =−a ₁(T _(a) −T _(i))−b ₁+γ  (1)

(whereas T₀≦T_(a)<T₁, a₁>0, and b₁>0)

y ₂ =−b ₂+γ  (2)

(whereas T₁≦T_(a)<T₂ and b₂>0)

y ₃ =a ₃(T _(a) −T _(i))+γ  (3)

(whereas T₂≦T_(a)<T₃ and a₃>0)

y ₄ =b ₄+γ  (4)

(whereas T₃≦T_(a)<T₄ and b₄>0)

y ₅ =−a ₅(T _(a)−T_(i))+b ₅+γ  (5)

(whereas T₄≦T_(a)≦T₅, a₅>0, b₅>0, a₁≈a₅, b₂≈b₄ and b₁≈b₅)

At this point, the center temperature T_(i) corresponds to theinflection point temperature of a quartz oscillator, and isapproximately 25° C. in a general quartz oscillator.

Now, the relationship between the sixth control voltage y₆ and the firstthrough third control voltages y₁, y₂ and y₃ and the relationshipbetween the seventh control voltage y₇, namely, the control voltage Vc,and the fourth through sixth control voltages y₄, y₃ and y₆ will bedescribed on the basis of the MAX circuit 14 a and the MIN circuit 14 bof FIG. 10.

In the MAX circuit 14 a, when the emitter currents of the first NPNtransistor Q1, the second NPN transistor Q2, the third NPN transistor Q3and the fourth NPN transistor Q7 are indicated as I_(EQ1), I_(EQ2),I_(EQ3) and I_(EQ7), respectively, the following relationship holds:

I _(EQ1) +I _(EQ2) +I _(EQ3) =I _(EQ7) =I ₁/2=I ₂  (6)

Also, the emitter currents of the respective NPN transistors arerepresented as follows:

I _(EQ1) =I _(SN) exp{(q/kT)·(y ₁ −V ₁)}  (7)

I _(EQ2) =I _(SN) exp{(q/kT)·(y ₂ −V ₁)}  (8)

I _(EQ3) =I _(SN) exp{(q/kT)·(y ₃ −V ₁)}  (9)

I _(EQ7) =I _(SN) exp{(q/kT)·(y ₆ −V ₁)}  (10)

wherein I_(SN) indicates a reverse saturation current of the NPNtransistor, q indicates a charge amount of electrons, k indicates theBoltzmann's constant, T indicates an absolute temperature, and V₁indicates the shared emitter potential of the NPN transistor.

Accordingly, when the formulas (7) through (10) are substituted for theformula (6) and the resultant formula is solved for y₆, the followingformula (11) representing the relationship between the sixth controlvoltage y₆ and the first through third control voltages y₁, y₂ and y₃can be obtained:

y ₆=(kT/q)·ln{exp(qy ₁ /kT)+exp(qy ₂ /kT)+exp(qy ₃ /kT)}  (11)

Similarly, in the MIN circuit 14 b, the emitter currents of the firstPNP transistor Q6, the second PNP transistor Q4, the third PNPtransistor Q5 and the fourth PNP transistor Q8 are indicated as I_(EQ6),I_(EQ4), I_(EQ5) and I_(EQ8), respectively, the following relationshipholds:

I _(EQ6) +I _(EQ4) +I _(EQ5) =I _(EQ8) =I ₃/2=I ₄  (12)

Furthermore, the emitter currents of the respective PNP transistors arerepresented as follows:

I _(EQ6) =I _(SP) exp{(q/kT)·(V ₂ −y ₆)}  (13)

I _(EQ4) =I _(SP) exp{(q/kT)·(V ₂ −y ₄)}  (14)

I _(EQ5) =I _(SP) exp{(q/kT)·(V ₂ −y ₅)}  (15)

I _(EQ8) =I _(SP) exp{(q/kT)·(V ₂ −y ₇)}  (16)

wherein I_(SP) indicates a reverse saturation current of the PNPtransistor, q indicates a charge amount of electrons, k indicates theBoltzmann's constant, T indicates an absolute temperature, and V₂indicates the shared emitter potential of the PNP transistor.

Accordingly, when the formulas (13) through (16) are substituted for theformula (12) and the resultant is solved for y₇, the following formula(17) representing the relationship between the seventh control voltagey₇ and the fourth through sixth control voltages y₄, y₅ and y₆ can beobtained:

 y ₇=(−kT/q)·ln{exp(−qy ₆ /kT)+exp(−qy ₄ /kT)+exp(−qy ₅ /kT)}  (17)

Furthermore, by substituting the sixth control voltage y₆ represented bythe formula (11) for the formula (17), the desired formula (18) can beobtained as follows:

y ₇=(−kT/q)·ln[1/{exp(qy ₁ /kT)+exp(qy ₂ /kT)+exp(qy ₃ /kT)}+exp(−qy ₄/kT)+exp(−qy ₅ /kT)]  (18)

Next, an exemplified configuration of the ROM/RAM circuit 16 of thisembodiment shown in FIG. 1 will be described.

FIG. 13 shows the circuit configuration of the ROM/RAM circuit 16 usedin the temperature compensating crystal oscillation device of thisembodiment. As is shown in FIG. 13, though it is merely one example, theROM/RAM circuit 16 includes a RAM data input circuit 161 as a serialdata input portion including serially connected four flip-flops, a PROMcircuit 162 including four programmable ROMs each receiving and storingeach bit of output data of the RAM data input circuit 161, and a switchcircuit 163 for externally receiving a selection signal SEL andselecting either the output data of the RAM data input circuit 161 oroutput data of the PROM circuit 162. In this case, the output data ofthe ROM/RAM circuit 16 is output, for example, to the current mirrorcircuit 33 of FIG. 5 as the 4-bit signal a₁ or the like. Although theexemplified ROM/RAM circuit 16 has a configuration for coping with 4-bitdata, the invention is not limited to this configuration and the bitnumber can be determined in accordance with the number of thetemperature compensating parameters described below.

The operation of the ROM/RAM circuit 16 will now be described withreference to a timing chart of RAM data input shown in FIG. 14.

First, in order to write desired data in the PROM circuit 162, a C/Esignal which corresponds to an enable signal in the RAM data inputcircuit 161 is activated so as to enable the data input, and aread/write signal W/R in the PROM circuit 162 is set in the write mode.Serial data of, for example, 1, 0, 1 and 1 are successively input fromthe data input terminal DATA to the RAM data input circuit 161 at a riseof a clock signal CLK. As a result, as is shown in FIG. 14, the firstoutput data “1” is output to the output terminal OUT1 of the firstflip-flop, the second output data “0” is output to the output terminalOUT2 of the second flip-flop, the third output data “1” is output to theoutput terminal OUT3 of the third flip-flop, and the fourth output data“1” is output to the output terminal OUT4 of the fourth flip-flop. Next,in the PROM circuit 162 of FIG. 13, the first output data is stored inthe PROM1, the second output data is stored in the PROM2, the thirdoutput data is stored in the PROM3 and the fourth output data is storedin the PROM4.

In order to directly output the data having been input to the RAM datainput circuit 161, the selection signal SEL in the switch circuit 163 isset at a level for passing the data through. In order to read the datastored in the PROM circuit 162, the selection signal SEL in the switchcircuit 163 is set at a level for selecting the PROM.

Modification 1 of Embodiment 1

A first modification of the first embodiment will now be described withreference to the accompanying drawing.

FIG. 15 shows the circuit configuration of a control circuit of acrystal oscillation device according to the first modification. In FIG.15, like reference numerals are used to refer to like elements used inthe control circuit of FIG. 10, and the description is omitted. Thecontrol circuit 14 of FIG. 15 includes a MAX circuit 14 c for receivingthe first control voltage y₁, the second control voltage y₂ and thethird control voltage y₃ generated by the constant voltage circuit 12and the temperature sensor circuit 13 of FIG. 1 and for outputting themaximum voltage among these control voltages as the sixth controlvoltage y₆; and a MIN circuit 14 d for receiving the fourth controlvoltage y₄ and the fifth control voltage y₅ generated by the constantvoltage circuit 12 and the temperature sensor circuit 13 of FIG. 1 andthe sixth control voltage y₆ output from the MAX circuit 14 c and foroutputting the minimum voltage among these control voltages as theseventh control voltage y₇.

In the MAX circuit 14 c, a first resistance R1 is serially connectedbetween the emitter of the first NPN transistor Q1 and the firstconstant current source I₁, a second resistance R2 is serially connectedbetween the emitter of the second NPN transistor Q2 and the firstconstant current source I₁, a third resistance R3 is serially connectedbetween the emitter of the third NPN transistor Q3 and the firstconstant current source I₁, and a fourth resistance R7 is seriallyconnected between the emitter of the fourth NPN transistor Q7 and thefirst constant current source I₁.

Similarly, in the MIN circuit 14 d, a fifth resistance R6 is seriallyconnected between the emitter of the first PNP transistor Q6 and thethird constant current source I₃, a sixth resistance R4 is seriallyconnected between the emitter of the second PNP transistor Q4 and thethird constant current source I₃, a seventh resistance R5 is seriallyconnected between the emitter of the third PNP transistor Q5 and thethird constant current source I₃, and an eighth resistance R8 isserially connected between the emitter of the fourth PNP transistor Q8and the third constant current source I₃.

In this modification, since the resistances are serially connected withthe emitters of the NPN transistors Q1, Q2, Q3 and Q7 in the MAX circuit14 c and the resistances are serially connected with the emitters of thePNP transistors Q6, Q4, Q5 and Q8 in the MIN circuit 14 d, theconnecting portions between the respective temperature regions in thecontrol voltage Vc shown in FIG. 12 can be smoothed. In general, incubic functional approximation using polygonal lines, an approximationerror Δf (=f−f₀) corresponding to a difference between the oscillationfrequency f after the temperature compensation and the referencefrequency f₀ of a quartz oscillator is largest at a connecting portionof the polygonal lines. However, the connecting portions between thetemperature regions can be thus smoothed, the approximation error can bereduced.

Modification 2 of Embodiment 1

A second modification of the first embodiment will now be described withreference to the accompanying drawings.

FIGS. 16(a) through 16(c) show the temperature dependency of anoscillation frequency attained by using a control circuit of a crystaloscillation device according to the second modification, wherein FIG.16(a) shows the temperature dependency of the oscillation frequencybefore the temperature compensation, FIG. 16(b) shows the temperaturedependency of a control voltage Vc used for the temperature compensationof a VCXO generated by the control circuit of this modification and FIG.16(c) shows the temperature dependency of a difference Δf between theoscillation frequency f attained after the temperature compensation byusing the control voltage Vc and a reference frequency f₀.

As a characteristic of this modification, the lines of the controlvoltages to be connected in the boundaries between the temperatureregions are smoothly connected in an analog manner by graduallytransforming the lines of the control voltages in accordance withtemperature change. Therefore, the generated control voltage can be moreapproximated to a cubic function, resulting in decreasing the differenceΔf in the oscillation frequency.

Furthermore, when the ambient temperature T_(a) is divided into threeregions of, T₀≦T_(a)<T₁, T₁≦T_(a)<T₂ and T₂≦T_(a)≦T₃, and straight linesy₁₁, y₁₂ and y₁₃ of three control voltages alone are used as is shown inFIG. 17, the same effect as is exhibited by the approximation using thefive straight lines y₁ through y₅ can be attained by making theconnecting portions smooth in an analog manner.

In the adjustment of the temperature compensation, decrease in thenumber of straight lines used for the polygonal lines approximation canbe a significant factor to decrease the storage capacity of the ROM/RAMcircuit, which will be described below.

Modification 3 of Embodiment 1

A third modification of the first embodiment will now be described.

The temperature characteristic of the oscillation frequency f of aquartz oscillator is point-symmetrical about the inflection pointtemperature T_(i) at a lower temperature side and a higher temperatureside as is shown in FIG. 11(a), and in this modification, thepoint-symmetry is used for generating a group of control voltages Vcwhich are point-symmetrical about the inflection point temperature T_(i)at the lower temperature side and the higher temperature side.

Specifically, in the aforementioned formulas (1) through (5)representing the first through fifth control voltages y₁ through y₅, theproportional coefficient a₁ of the formula (1) is equal to theproportional coefficient a₅ of the formula (5), the constant b₁ of theformula (1) is equal to the constant b₅ of the formula (5), and theconstant b₂ of the formula (2) is equal to the constant b₄ of theformula (4).

In this manner, the circuit constant of one internal element of thecontrol circuit 14 which determines the temperature characteristic atthe lower temperature side and the higher temperature side can bedesigned by using a predetermined proportion to the circuit constant ofanother internal element, and hence, the storage capacity of the ROM/RAMcircuit 16 can be largely decreased.

At this point, the control voltage Vc for the temperature compensationof a quartz oscillator is assumed to be represented by the followingcubic function:

Vc=α(T−T _(i))³+β(T−T _(i))+γ  (19)

wherein α indicates a negative cubic temperature coefficient, βindicates a linear temperature coefficient, γ is a constantcorresponding to a voltage difference from a voltage for attaining areference frequency at an inflection point temperature, T indicates anabsolute temperature and T_(i) indicates the inflection pointtemperature corresponding to an inflection point of the cubic function.

FIG. 18 is a table listing memory capacities of the ROM/RAM circuitrequired by various control circuit systems. In the case where theparameter for adjusting the temperature compensation of the controlvoltage is limited to the parameter α of the cubic temperaturecharacteristic, in order to dependently adjust the temperaturecompensating parameters of the first through fifth control voltages y₁through y₅ and attain the stability of the oscillation frequency f of±2.5 ppm in the desired temperature range, each of the proportionalcoefficients a₁, a₃ and a₅ requires 4 bits, each of the constants b₁ andb₅ requires 4 bits, and each of the constants b₂ and b₄ requires 2 bitsin the aforementioned formulas (1) through (5). As a result, a D/Aconverter of 24 bits in total is required.

However, when the control voltage is point-symmetrical at the lowertemperature side and the higher temperature side as in thismodification, the bits for adjusting the constants a₅, b₅ and b₄ are notnecessary because a₁, =a₅, b₁=b₅ and b₂=b₄. As a result, the temperaturecompensation can be adjusted by a D/A converter of 14 bits in total.

Modification 4 of Embodiment 1

A fourth modification of the first embodiment will now be described withreference to the accompanying drawings.

FIGS. 19(a) and 19(b) show the temperature dependency of a controlvoltage output by a control circuit of a crystal oscillation deviceaccording to a fourth modification of the first embodiment, wherein FIG.19(a) shows cubic curves f₁, f₂ and f₃ attained by different cubictemperature coefficients α in the oscillation frequency of a quartzoscillator and FIG. 19(b) shows control voltages Vc1, Vc2 and Vc3 forcompensating the corresponding cubic curves.

In this modification, the temperature coefficients (proportionalcoefficients) of the temperature characteristics of the control voltagegroup including the first through fifth control voltages y₁ through y₅and varied in the shape of polygonal lines in accordance with thetemperature are provided with predetermined proportions to one another.

Thus, in determining the various parameters such as the circuit constantof the control circuit 14, the parameter of one internal element can bedesigned by using the predetermined proportion to the parameter ofanother internal element. As a result, the memory capacity of theROM/RAM circuit 16 can be largely decreased.

Now, optimal proportions for minimizing the approximation error betweenthe cubic temperature coefficient α and the control voltages y₁ throughy₅ will be specifically introduced. When the control voltage peculiar toa quartz oscillator is assumed to be an ideal control voltage Vci, theformula (19) is changed into the following formula (20):

Vci=α(T−T _(i))³+β(T−T _(i))+γ  (20)

With the operating temperature range of the crystal oscillation deviceindicated as T_(o), the ideal control voltage Vci is separated into alinear function Vci1 represented by the formula (25) and a cubicfunction vci3 represented by the formula (26), both of which passthrough three points represented by the following formulas (21) through(23), and the cubic function vci3 is subjected to the polygonal linesapproximation:

[T, Vci]=[(T _(i) −T _(o)), Vci(T _(i) −T _(o))]  (21)

[T, Vci]=[T _(i), γ]  (22)

[T, Vci]=[(T _(i) +T _(o)), Vci(T _(i) +T _(o))]  (23)

Vci=Vci 1 +Vci 3  (24)

Vci 1=(β+αT _(o) ²) (T−T _(i))+γ  (25)

Vci 3=α(T−T _(i))³ −αT _(o) ²(T−T _(i))  (26)

The linear function Vci1 and the cubic function Vci3 are shown in FIGS.20(a) through 20(c). A line 1 indicates the linear function Vci1 and acurve 2 indicates the cubic function Vci3 in FIG. 20(a), merely thelinear function Vci1 is shown in FIG. 20(b), and FIG. 20(c) shows thepolygonal lines approximation of the cubic function Vci3 shown as thecurve 2 by using a group of lines y₁ through y₅ corresponding to thefive control voltages of the embodiment.

At this point, the approximation error in the polygonal linesapproximation is minimized in each region in the following cases: In thefirst temperature region (T_(i)−T_(o)≦T<T_(i)−0.755T_(o)), it isminimized when the first control voltage y₁ is: $\begin{matrix}{y_{1} = {{{- 1.46}\alpha \quad {T_{o}^{2}\left( {T - T_{i}} \right)}} - {1.46\alpha \quad T_{o}^{3}}}} & (27) \\{= {{- {a_{1}\left( {T - T_{i}} \right)}} - b_{1}}} & (28)\end{matrix}$

In the second temperature region (T_(i)−0.755T_(o)≦T<T_(i)−0.398T_(o)),it is minimized when the second control voltage y₂ is: $\begin{matrix}{y_{2} = {{- 0.358}\alpha \quad T_{o}^{3}}} & (29) \\{= {- b_{2}}} & (30)\end{matrix}$

In the third temperature region (T_(i)−0.398T_(o)≦T<T_(i)+0.398T_(o)),it is minimized when the third control voltage y₃ is: $\begin{matrix}{y_{3} = {0.9\alpha \quad {T_{o}^{2}\left( {T - T_{i}} \right)}}} & (31) \\{= {a_{3}\left( {T - T_{i}} \right)}} & (32)\end{matrix}$

In the fourth temperature region (T_(i)+0.398T_(o)≦T<T_(i)+0.755T_(o)),it is minimized when the fourth control voltage y₄ is: $\begin{matrix}{y_{4} = {0.358\alpha \quad T_{o}^{3}}} & (33) \\{= b_{4}} & (34)\end{matrix}$

In the fifth temperature region (T_(i)+0.755T_(o)≦T≦T_(i)+T_(o)), it isminimized when the fifth control voltage y₅ is: $\begin{matrix}{y_{5} = {{{- 1.46}\alpha \quad {T_{o}^{2}\left( {T - T_{i}} \right)}} + {1.46\alpha \quad T_{o}^{3}}}} & (35) \\{= {{- {a_{5}\left( {T - T_{i}} \right)}} + b_{5}}} & (36)\end{matrix}$

FIG. 21(a) shows the cubic function Vci3 of the formula (26), the firstcontrol voltage y₁ of the formula (27), the second control voltage y₂ ofthe formula (29), the third control voltage y₃ of the formula (31), thefourth control voltage y₄ of the formula (33), and the fifth controlvoltage y₅ of the formula (35). FIG. 21(b) shows a difference ΔVcbetween the ideal control voltage Vci3 shown in FIG. 21(a) and anapproximation control voltage Vcp obtained through the polygonal linesapproximation using the control voltages y₁ through y₅.

Then, the coefficients of the approximation control voltage Vcp arecollected on the left side and the coefficients of the ideal controlvoltage Vci are collected on the right side. When the coefficients ofthe formula (27) and (28) and the coefficients of the formulas (35) and(36) are compared, the following are obtained:

a ₁ =a ₅=1.46αT _(o) ²  (37)

b ₁ =b ₅=1.46αT _(o) ³  (38)

when the coefficients of the formulas (31) and (32) are compared, thefollowing is obtained:

a ₃=0.9αT _(o) ²  (39)

When the coefficients of the formulas (29) and (30) and the coefficientsof the formulas (33) and (34) are compared, the following is obtained:

b ₂ =b ₄=0.358αT _(o) ³  (40)

By transforming the formulas (37) through (40), the formulasrepresenting the desired proportions between the cubic temperaturecoefficient α and the proportional coefficients of the lines used forthe polygonal lines approximation can be obtained as follows:

a ₁/α=1.46T _(o) ²  (41)

a ₃/α=0.9T _(o) ²  (42)

a ₅/α=1.46T _(o) ²  (43)

b ₁/α=1.46T _(o) ³  (44)

b ₂/α=0.358T _(o) ³  (45)

b ₄/α=0.358T _(o) ³  (46)

b ₅/α=1.46T _(o) ³  (47)

At this point, when the inflection point temperature is assumed to be25° C. and the operating temperature range T_(o) is 60 degree, theambient temperature T_(a) in this modification is −35° C. through +85°C.

In this manner, even when each quartz oscillator has a different cubiccoefficient α of the ideal control voltage Vci, the proportions of α arenot varied respectively in a₁/α, a₃/α, a₅/α, b₁/α, b₂/α, b₄/α and b₅/α.

Accordingly, in this modification, the proportional coefficients a₁, a₃and a₅ of the lines and the constants b₁, b₂, b₄ and b₅ of the lines arerespectively provided with the proportions as is shown in the formulas(41) through (47). In this manner, in the adjustment of the cubictemperature coefficient α of a quartz oscillator, the circuit constantscorresponding to the proportional coefficients a₁, a₃ and a₅ and thecircuit constants corresponding to the constants b₁, b₂, b₄ and b₅ canbe set in a batch, and hence, the adjustment can be performed by a D/Aconverter of 6 bits in total as is shown in FIG. 18. Therefore, evenwhen the memory capacity of the ROM/RAM circuit 16 is small,fluctuations of the cubic temperature coefficient and the lineartemperature coefficient derived from a cut angle of the AT cut of aquartz oscillator and fluctuation of the absolute value of theoscillation frequency can be both definitely adjusted.

Embodiment 2

A second embodiment of the invention will now be described withreference to the accompanying drawings.

FIG. 22 is a functional block diagram of a function generator for thetemperature compensation used in a temperature compensating crystaloscillation device according to the second embodiment. As is shown inFIG. 22, the function generator includes a MAX/MIN circuit 14A havingthe same configuration as the control circuit 14 of the first embodimentfor receiving the outputs of a constant voltage circuit 12 and atemperature sensor circuit 13 and for generating a cubic control voltageαVc corresponding to the cubic temperature characteristic parameter αwithin a predetermined temperature range in the control voltage Vc forthe temperature compensation represented by the formula (19); a lineartemperature characteristic generating circuit 17 for receiving theoutput of the temperature sensor circuit 13 and for generating a linearcontrol voltage βVc corresponding to a linear temperature characteristicparameter β within a predetermined temperature range in the controlvoltage Vc for the temperature compensation represented by the formula(19); a zero-order temperature characteristic generating circuit 18 forreceiving the output of the constant voltage circuit 12 and forgenerating a zero-order control voltage γ Vc corresponding to thezero-order temperature characteristic parameter γ within a predeterminedtemperature range in the control voltage Vc for the temperaturecompensation represented by the formula (19), namely, independent of thetemperature within a predetermined temperature; and a T_(i) adjustingcircuit 19 for receiving the output of the temperature sensor circuit13, adjusting the value of an inflection point temperature T_(i) shownin the formula (19) and outputting the adjusted value to the MAX/MINcircuit 14A and the linear temperature characteristic generating circuit17.

In the function generator for generating the control voltage Vc for thetemperature compensation of a VCXO of this embodiment, the controlvoltage Vc is generated by obtaining a sum of the output voltage α Vc ofthe MAX/MIN circuit 14A for performing, with the ambient temperatureT_(a) divided into five regions, the polygonal lines approximation usinga linear function in each region, the output voltage β Vc of the lineartemperature characteristic generating circuit 17 for adjusting thelinear characteristic of the temperature compensating parameter, and theoutput voltage γ Vc of the zero-order temperature characteristicgenerating circuit 18 for adjusting the zero-order characteristic of thetemperature compensating parameter, namely, a voltage difference,independent of the ambient temperature T_(a), from the voltage forattaining a reference frequency at the inflection point temperature.Accordingly, the temperature compensation of the oscillation frequencyof a quartz oscillator can be definitely carried out in the entire rangeof the ambient temperature T_(a).

FIGS. 23(a) through 23(d) are graphs for illustrating variation of thecontrol voltage Vc through the adjustment of the temperaturecompensating parameters α, β, and γ and the inflection point temperatureT_(i). FIG. 23(a) shows the variation derived from the cubic temperaturecharacteristic parameter α, FIG. 23(b) shows the variation derived fromthe linear temperature characteristic parameter β, FIG. 23(c) shows thevariation derived from the zero-order temperature characteristicparameter γ, namely, the voltage difference from the voltage forattaining the reference frequency at the inflection point temperature,and FIG. 23(d) shows the variation derived from the inflection pointtemperature T_(i).

As is shown in FIG. 23(a), when the cubic temperature characteristicparameter α is changed, the absolute values at the minimum point and themaximum point are decreased, and as is shown in FIG. 23(b), when thelinear temperature characteristic parameter β is changed, thetemperature characteristic is rotated about the inflection pointtemperature T_(i) (i.e., the inflection point). Also, as is shown inFIG. 23(c), when the zero-order temperature characteristic parameter γis changed, the so-called y-intercept is moved. Furthermore, as is shownin FIG. 23(d), when the inflection point temperature T_(i) is changed,the characteristic graph is moved in the X-axis direction.

Embodiment 3

A third embodiment of the invention will now be described with referenceto the accompanying drawings.

FIG. 24 is a functional block diagram for illustrating the adjustment ofan oscillation frequency in a temperature compensating crystaloscillation device according to the third embodiment. In FIG. 24, likereference numerals are used to refer to like elements shown in FIG. 1,and the description is omitted. In this embodiment, the constant voltagecircuit 12, the temperature sensor circuit 13, the control circuit 14,the VCXO 15 and the ROM/RAM circuit 16 as optimizing means have theconfigurations equivalent to those of the first embodiment. Furthermore,as is shown in FIG. 24, the temperature compensating crystal oscillationdevice 10A of this embodiment is provided with a switch SW1 forconnecting/disconnecting the control circuit 14 and the VCXO 15.

In general, each quartz oscillator included in the VCXO 15 hasfluctuation in the AT cut angle, the frequency difference from areference frequency at an inflection point temperature and theinflection point temperature T_(i). Therefore, it is necessary to adjustthe oscillation frequency of the VCXO 15 within a range of ±2.5 ppmbefore shipping.

The crystal oscillation device of this embodiment has the switch SW1between the control circuit 14 and the VCXO 15. Therefore, the crystaloscillation device can definitely cope with a RAM mode and a ROM mode asfollows: In the RAM mode, externally input data including thetemperature compensating parameters are input to the RAM data inputcircuit 161 of the ROM/RAM circuit 16 through the external data inputterminal DATA and the control voltage Vc is adjusted by using the dataof the RAM data input circuit 161, so as to determine an optimal voltagecharacteristic. In the ROM mode, data selected in the RAM mode arewritten in a ROM portion of the ROM/RAM circuit 16 and the ROM data areread under actual use conditions, so as to output a control voltage Vcin accordance with the ambient temperature T_(a).

The method of adjusting the oscillation frequency of the temperaturecompensating crystal oscillation device 10A having the aforementionedconfiguration will now be described with reference to the accompanyingdrawing.

FIG. 25 is a flowchart for the method of adjusting the crystaloscillation device of this embodiment.

First, in a peculiar control voltage measuring step ST1, the switch SW1of FIG. 24 is opened, one input terminal of a PLL circuit 51 isconnected with the output terminal fout of the VCXO 15, and apredetermined frequency f0 independent of the ambient temperature isinput to the other input terminal of the PLL circuit 51. Thus, anexternal control voltage Vcext is adjusted so that the oscillationfrequency f output from the output terminal fout can be equal to thepredetermined frequency f0. Then, after the crystal oscillation device10A to be adjusted is placed in a constant temperature oven, theexternal control voltage Vcext is measured with the ambient temperaturechanged from a low temperature to a high temperature. In this manner, apeculiar control voltage Vc0, that is, an ideal control voltage at whichthe variation of the oscillation frequency f of the VCXO 15 caused bythe temperature is 0, is obtained.

Next, in a peculiar parameter determining step ST2, on the basis of thetemperature characteristic of the peculiar control voltage Vc0,parameters of a control signal corresponding to the cubic temperaturecoefficient, the linear temperature coefficient, the frequencydifference from the reference frequency at the inflection pointtemperature and the inflection point temperature are calculated, andpeculiar parameters are defined as α₀, β₀, γ₀ and T_(i0), respectively.

Then, in an initial control voltage characteristic measuring step ST3, aswitch SW2 is opened with the switch SW1 short-circuited and the deviceis set in the RAM mode. Then, the temperature characteristic of aninitial control voltage Vc1 of the control circuit 14 is measured aswell as change of the temperature characteristic of the initial controlvoltage Vc1 in accordance with change of data corresponding to therespective parameters input to the RAM is measured.

Next, in an initial parameter determining step ST4, on the basis of thetemperature characteristic of the initial control voltage Vc1,parameters for initial temperature compensation of the initial controlvoltage Vc1 corresponding to the cubic temperature coefficient, thelinear temperature coefficient, the frequency difference from thereference frequency at the inflection point temperature and theinflection point temperature of the quartz oscillator are calculated anddefined as α₁, β₁, γ₁ and T_(i1), respectively.

Subsequently, in a temperature compensating parameter change calculatingstep ST5, the amounts of change corresponding to 1 bit of the respectiveparameters as the RAM data are calculated and defined as Δα, Δβ, Δγ,ΔT_(i), respectively.

Then, in apeculiar parameter/initial parameter difference calculatingstep ST6, differences in the corresponding parameters between α₀, β₀, γ₀and T_(i0) and α₁, β₁, γ₁ and T_(i1) are calculated.

Next, in an optimal parameter determining step ST7, on the basis of Δα,Δβ, Δγ and ΔT_(i) calculated in the temperature compensating parameterchange calculating step ST5, optimal parameters are determined so thatthe differences in the parameters calculated in the peculiarparameter/initial parameter difference calculating step ST6 can beapproximated to zero.

Then, in an oscillation frequency characteristic confirming step ST8,the determined optimal parameters are written in the PROM circuit 162,and the device is set in the ROM mode. Then, the crystal oscillationdevice 10A to be adjusted is placed in a constant temperature ovenagain, and the temperature characteristic of the oscillation frequency fis measured, so as to confirm that the temperature dependency is setwithin a predetermined range. In the case where the temperaturedependency exceeds the predetermined range, the procedure returns to anappropriate upstream step, and re-adjustment is carried out.

In this manner, according to this embodiment, the adjustment forsuppressing the temperature dependency of the oscillation frequencywithin a predetermined range can be definitely realized with regard tothe fluctuation of the AT cut angle, the fluctuation of the frequencydifference from the reference frequency at the inflection pointtemperature and the fluctuation of the inflection point temperature of aquartz oscillator.

Moreover, the procedures of the peculiar control voltage measuring stepST1, the peculiar parameter determining step ST2, the initial controlvoltage characteristic measuring step ST3, the initial parameterdetermining step ST4, the temperature compensating parameter changecalculating step ST5, the peculiar parameter/initial parameterdifference calculating step ST6, the optimal parameter determining stepST7 and the oscillation frequency characteristic confirming step ST8 canbe automatically performed by using a personal computer or the like.Therefore, by writing optimal parameters in accordance with each quartzoscillator in the ROM and automatically confirming the oscillationfrequency by using the ROM data, time required for the entire processfor adjusting the crystal oscillation device can be largely decreasedand the accuracy can be remarkably improved.

What is claimed is:
 1. A function generator comprising: a first analogsignal generating circuit for generating and outputting a predeterminedanalog signal substantially independent of an ambient temperature; asecond analog signal generating circuit for generating and outputting ananalog signal dependent upon the ambient temperature; storage means forstoring control information respectively corresponding to first, second,third, fourth and fifth temperature regions obtained by dividing afeasible range of the ambient temperature into five continuous parts inthis order along a direction from a low temperature to a hightemperature; a third analog signal generating circuit for receiving saidsignal from said first analog signal generating circuit and said signalfrom said second analog signal generating circuit and further receivingsaid control information from said storage means, and for generating andoutputting first, second, third, fourth and fifth control signalsrespectively corresponding to said five temperature regions; and acontrol circuit for receiving said first through fifth control signalsand generating to output a control signal as a function of a temperaturebased on each received signal, wherein said storage means stores as saidcontrol information: a first proportional value defining a relationshipbetween a proportional coefficient between a temperature used forgenerating said first control signal and the output value thereof and acubic coefficient of a temperature characteristic of an oscillationfrequency of a quartz oscillator; a second proportional value defining arelationship between a constant between a temperature used forgenerating said second control signal and the output value thereof andsaid cubic coefficient; a third proportional value defining arelationship between a proportional coefficient between a temperatureused for generating said third control signal and the output valuethereof and said cubic coefficient; a fourth proportional value defininga relationship between a constant between a temperature used forgenerating said fourth control signal and the output value thereof andsaid cubic coefficient; and a fifth proportional value defining arelationship between a proportional coefficient between a temperatureused for generating said fifth control signal and the output valuethereof and said cubic coefficient, and wherein when the ambienttemperature is in any of said first, second and third temperatureregions, said control signal outputted from said control circuitcomprises: any of said first, second and third control signals which isselected by said control circuit; and another signal generated byaltering said selected signal so as to form a smooth curve in a regionaround a border between the temperature region to which the ambienttemperature belongs and the adjacent temperature region, while when theambient temperature is in either of said fourth and fifth temperatureregions, said control signal outputted from said control circuitcomprises: any of at least one of said first, second and third controlsignals including said third control signal, said fourth control signaland said fifth control signal which is selected by said control circuit;and another signal generated by altering said selected signal so as toform a smooth curve in a region around a border between the temperatureregion to which the ambient temperature belongs and the adjacenttemperature region.
 2. The function generator of claim 1, wherein saidcontrol circuit includes: a first NPN transistor whose collector issupplied with a supply voltage, whose base is supplied with a firstelectric signal decreasing in proportion to the ambient temperature andwhose emitter is connected with an input of a first current source; asecond NPN transistor whose collector is supplied with the supplyvoltage, whose base is supplied with a second electric signal retaininga predetermined value independent of the ambient temperature and whoseemitter is connected with the input of said first current source; athird NPN transistor whose collector is supplied with the supplyvoltage, whose base is supplied with a third electric signal increasingin proportion to the ambient temperature and whose emitter is connectedwith the input of said first current source; a fourth NPN transistorwhose collector and base are connected with an output of a secondcurrent source having a current value a half as large as a current valueof said first current source and whose emitter is connected with theinput of said first current source; a first PNP transistor whose base isconnected with the collector of said fourth NPN transistor, whoseemitter is connected with an output of a third current source and whosecollector is grounded; a second PNP transistor whose base is suppliedwith a fourth electric signal retaining a predetermined valueindependent of the ambient temperature, whose emitter is connected withthe output of said third current source and whose collector is grounded;a third PNP transistor whose base is supplied with a fifth electricsignal decreasing in proportion to the ambient temperature, whoseemitter is connected with the output of said third current source andwhose collector is grounded; and a fourth PNP transistor whose emitteris connected with the output of said third current source and whosecollector and base are connected with an input of a fourth currentsource having a current value a half as large as a current value of saidthird current source, said fourth NPN transistor selects an electricsignal having a maximum voltage value among said first electric signal,said second electric signal and said third electric signal and outputssaid selected electric signal at the collector thereof as a sixthelectric signal, said fourth PNP transistor selects an electric signalhaving a minimum voltage value among said fourth electric signal, saidfifth electric signal and said sixth electric signal and outputs saidselected electric signal at the collector thereof as a seventh electricsignal, and said control circuit outputs said seventh electric signal assaid control signal.
 3. The function generator of claim 2, wherein afirst resistance is serially connected between the emitter of said firstNPN transistor and said first current source, a second resistance isserially connected between the emitter of said second NPN transistor andsaid first current source, a third resistance is serially connectedbetween the emitter of said third NPN transistor and said first currentsource, a fourth resistance is serially connected between the emitter ofsaid fourth NPN transistor and said first current source, a fifthresistance is serially connected between the emitter of said first PNPtransistor and said third current source, a sixth resistance is seriallyconnected between the emitter of said second PNP transistor and saidthird current source, a seventh resistance is serially connected betweenthe emitter of said third PNP transistor and said third current source,and an eighth resistance is serially connected between the emitter ofsaid fourth PNP transistor and said third current source.
 4. A functiongenerator of claim 1, wherein said control circuit comprises: a MAXcircuit receiving said first, second and third control signals, andoutputting any of said first, second and third control signals,whichever has a maximum value at a given temperature within any of saidfirst, second and third temperature regions; and a MIN circuit receivingsaid fourth control signal, said fifth control signal and the signaloutputted from said MAX circuit, and outputting any of said fourthcontrol signal, said fifth control signal and the control signaloutputted from said MAX circuit, whichever has a minimum value at agiven temperature within either of said fourth and fifth temperatureregions, and wherein said control signal outputted from said controlcircuit is the signal outputted from said MIN circuit.
 5. A functiongenerator of claim 1, wherein said control circuit comprises: a MAXcircuit including a first differential amplification circuit with afirst set of three input terminals for receiving said first, second andthird control signals, respectively, and outputting a signalcorresponding to a signal obtained by dividing each of said first,second and third control signals based on a resistance of each of nodesat which transistor circuits composing said first differentialamplification circuit and each of said first set of input terminals arecommonly connected; and a MIN circuit including a second differentialamplification circuit with a second set of three input terminals forreceiving said fourth control signal, said fifth control signal and thesignal outputted from said MAX circuit, and outputting a signalcorresponding to a signal obtained by dividing each of said fourthcontrol signal, said fifth control signal and the signal outputted fromsaid MAX circuit based on a resistance of other nodes at which othertransistor circuits composing said second differential amplificationcircuit and each of said second set of input terminals are commonlyconnected, and wherein said control signal outputted from said controlcircuit is the signal outputted from said MIN circuit.
 6. A functiongenerator of claim 1, wherein said control circuit comprises: a MINcircuit receiving said third, fourth and fifth control signals, andoutputting any of said third, fourth and fifth control signals,whichever has a minimum value at a given temperature within any of saidthird, fourth and fifth temperature regions; and a MAX circuit receivingsaid first control signal, said second control signal and the signaloutputted from said MIN circuit, and outputting any of said firstcontrol signal, said second control signal and the signal outputted fromsaid MIN circuit, whichever has a maximum value at a given temperaturewithin either of said first and second temperature regions, and whereinsaid control signal outputted from said control circuit is the signaloutputted from said MAX circuit.
 7. A function generator of claim 1,wherein said control circuit comprises: a MIN circuit including a firstdifferential amplification circuit with a first set of three inputterminals for receiving said third, fourth and fifth control signals,respectively, and outputting a signal corresponding to a signal obtainedby dividing each of said third, fourth and fifth control signals basedon a resistance of each of nodes at which transistor circuits composingsaid first differential amplification circuit and each of said first setof input terminals are commonly connected; and a MAX circuit including asecond differential amplification circuit with a second set of threeinput terminals for receiving said first control signal, said secondcontrol signal and the signal outputted from said MIN circuit, andoutputting a signal corresponding to a signal obtained by dividing eachof said first control signal, said second control signal and the signaloutputted from said MIN circuit based on a resistance of each of othernodes at which other transistor circuits composing said seconddifferential amplification circuit and each of said second set of inputterminals are commonly connected, and wherein said control signaloutputted from said control circuit is said signal outputted from saidMAX circuit.
 8. A function generator of claim 1, wherein said storagemeans comprises: a RAM data input circuit; a ROM circuit; and a switchcircuit, said RAM data input circuit performing a parallel conversion ona serial data received from outside based on a clock signal when anoperation enable signal indicates that operation is permitted, togenerate a plurality of parallel data, and outputting said parallel datato said ROM circuit and said switch circuit; a PROM circuit storing saidparallel data received from said RAM data input circuit at a datastorage circuit included in said PROM circuit when a read/write controlsignal indicates that write operation is permitted, while outputtingsaid parallel data to said switch circuit when said read/write controlsignal indicates that read operation is permitted; and said switchcircuit selecting either of said parallel data outputted from said RAMdata input circuit and from said PROM circuit, and outputting saidselected parallel data.
 9. A crystal oscillation device comprising: afirst analog signal generating circuit for generating and outputting apredetermined analog signal substantially independent of an ambienttemperature; a second analog signal generating circuit for generatingand outputting an analog signal dependent upon the ambient temperature;storage means for storing control information respectively correspondingto first, second, third, fourth and fifth temperature regions obtainedby dividing a feasible range of the ambient temperature into fivecontinuous parts in this order along a direction from a low temperatureto a high temperature; a third analog signal generating circuit forreceiving said signal from said first analog signal generating circuitand said signal from said second analog signal generating circuit andfurther receiving said control information from said storage means, andfor generating to output first, second, third, fourth and fifth controlsignals respectively corresponding to said five temperature regions; acontrol circuit for receiving said first through fifth control signalsand generating to output a control signal as a function of a temperaturebased on each received signal; and a crystal oscillating circuit forreceiving a control signal from said control circuit so as to becontrolled to have an oscillation frequency at a predetermined value bysaid control signal, wherein said storage means stores as said controlinformation: a first proportional value defining a relationship betweena proportional coefficient between a temperature used for generatingsaid first control signal and the output value thereof and a cubiccoefficient of a temperature characteristic of an oscillation frequencyof a quartz oscillator; a second proportional value defining arelationship between a constant between a temperature used forgenerating said second control signal and the output value thereof andsaid cubic coefficient; a third proportional value defining arelationship between a proportional coefficient between a temperatureused for generating said third control signal and the output valuethereof and said cubic coefficient; a fourth proportional value defininga relationship between a constant between a temperature used forgenerating said fourth control signal and the output value thereof andsaid cubic coefficient; and a fifth proportional value defining arelationship between a proportional coefficient between a temperatureused for generating said fifth control signal and the output valuethereof and said cubic coefficient, and wherein when the ambienttemperature is in any of said first, second and third temperatureregions, said control signal outputted from said control circuitcomprises: any of said first, second and third control signals which isselected by said control circuit; and another signal generated byaltering said selected signal so as to form a smooth curve in a regionaround a border between the temperature region to which the ambienttemperature belongs and the adjacent temperature region, while when theambient temperature is in either of said fourth and fifth temperatureregions, said control signal outputted from said control circuitcomprises: any of at least one of said first, second and third controlsignals including said third control signal, said fourth control signaland said fifth control signal which is selected by said control circuit;and another signal generating by altering said selected signal so as toform a smooth curve in a region around a border between the temperatureregion to which the ambient temperature belongs and the adjacenttemperature region.
 10. The crystal oscillation device of claim 9,wherein said control circuit includes: a first NPN transistor whosecollector is supplied with a supply voltage, whose base is supplied witha first electric signal decreasing in proportion to the ambienttemperature and whose emitter is connected with an input of a firstcurrent source; a second NPN transistor whose collector is supplied withthe supply voltage, whose base is supplied with a second electric signalretaining a predetermined value independent of the ambient temperatureand whose emitter is connected with the input of said first currentsource; a third NPN transistor whose collector is supplied with thesupply voltage, whose base is supplied with a third electric signalincreasing in proportion to the ambient temperature and whose emitter isconnected with the input of said first current source; a fourth NPNtransistor whose collector and base are connected with an output of asecond current source having a current value a half as large as acurrent value of said first current source and whose emitter isconnected with the input of said first current source; a first PNPtransistor whose base is connected with the collector of said fourth NPNtransistor, whose emitter is connected with an output of a third currentsource and whose collector is grounded; a second PNP transistor whosebase is supplied with a fourth electric signal retaining a predeterminedvalue independent of the ambient temperature, whose emitter is connectedwith the output of said third current source and whose collector isgrounded; a third PNP transistor whose base is supplied with a fifthelectric signal decreasing in proportion to the ambient temperature,whose emitter is connected with the output of said third current sourceand whose collector is grounded; and a fourth PNP transistor whoseemitter is connected with the output of said third current source andwhose collector and base are connected with an input of a fourth currentsource having a current value a half as large as a current value of saidthird current source, said fourth NPN transistor selects an electricsignal having a maximum voltage value among said first electric signal,said second electric signal and said third electric signal and outputssaid selected electric signal at the collector thereof as a sixthelectric signal, said fourth PNP transistor selects an electric signalhaving a minimum voltage value among said fourth electric signal, saidfifth electric signal and said sixth electric signal and outputs saidselected electric signal at the collector thereof as a seventh electricsignal, and said control circuit outputs said seventh electric signal assaid control signal.
 11. The crystal oscillation device of claim 10,wherein a first resistance is serially connected between the emitter ofsaid first NPN transistor and said first current source, a secondresistance is serially connected between the emitter of said second NPNtransistor and said first current source, a third resistance is seriallyconnected between the emitter of said third NPN transistor and saidfirst current source, a fourth resistance is serially connected betweenthe emitter of said fourth NPN transistor and said first current source,a fifth resistance is serially connected between the emitter of saidfirst PNP transistor and said third current source, a sixth resistanceis serially connected between the emitter of said second PNP transistorand said third current source, a seventh resistance is seriallyconnected between the emitter of said third PNP transistor and saidthird current source, and an eighth resistance is serially connectedbetween the emitter of said fourth PNP transistor and said third currentsource.
 12. The crystal oscillation device of claim 9, wherein saidstorage means comprises a RAM circuit and a ROM circuit: said RAMcircuit storing parameters for compensating the temperature dependencyof the oscillation frequency of said crystal oscillating circuit, ofsaid first through fifth control signals output by said control circuit,with varying each of said parameters with regard to each of said controlsignals; and said ROM circuit being programmable and storing an optimalparameter of said parameters with regard to each of said controlsignals.
 13. The crystal oscillation device of claim 9, furthercomprising: optimizing means for optimizing said control signals outputby said control circuit independently of one another and in accordancewith a cubic temperature coefficient, a linear temperature coefficient,a frequency difference from a reference frequency at a temperature of aninflection point and said temperature of the inflection point of thetemperature dependency of the oscillation frequency of said crystaloscillating circuit.
 14. A crystal oscillation device of claim 9,wherein said control circuit comprises: a MAX circuit receiving saidfirst, second and third control signals, and outputting any of saidfirst, second and third control signals, whichever has a maximum valueat a given temperature within any of said first, second and thirdtemperature regions; and a MIN circuit receiving said fourth controlsignal, said fifth control signal and the signal outputted from said MAXcircuit, and outputting any of said fourth control signal, said fifthcontrol signal and the control signal outputted from said MAX circuit,whichever has a minimum value at a given temperature within either ofsaid fourth and fifth temperature regions, and wherein said controlsignal outputted from said control circuit is the signal outputted fromsaid MIN circuit.
 15. A crystal oscillation device of claim 9, whereinsaid control circuit comprises: a MAX circuit including a firstdifferential amplification circuit with a first set of three inputterminals for receiving said first, second and third control signals,respectively, and outputting a signal corresponding to a signal obtainedby dividing each of said first, second and third control signals basedon a resistance of each of nodes at which transistor circuits composingsaid first differential amplification circuit and each of said first setof input terminals are commonly connected; and a MIN circuit including asecond differential amplification circuit with a second set of threeinput terminals for receiving said fourth control signal, said fifthcontrol signal and the signal outputted from said MAX circuit, andoutputting a signal corresponding to a signal obtained by dividing eachof said fourth control signal, said fifth control signal and the signaloutputted from said MAX circuit based on a resistance of other nodes atwhich other transistor circuits composing said second differentialamplification circuit and each of said second set of input terminals arecommonly connected, and wherein said control signal outputted from saidcontrol circuit is the signal outputted from said MIN circuit.
 16. Acrystal oscillation device of claim 9, wherein said control circuitcomprises: a MIN circuit receiving said third, fourth and fifth controlsignals, and outputting any of said third, fourth and fifth controlsignals, whichever has a minimum value at a given temperature within anyof said third, fourth and fifth temperature regions; and a MAX circuitreceiving said first control signal, said second control signal and thesignal outputted from said MIN circuit, and outputting any of said firstcontrol signal, said second control signal and the signal outputted fromsaid MIN circuit, whichever has a maximum value at a given temperaturewithin either of said first and second temperature regions, and whereinsaid control signal outputted from said control circuit is the signaloutputted from said MAX circuit.
 17. A crystal oscillation device ofclaim 9, wherein said control circuit comprises: a MIN circuit includinga first differential amplification circuit with a first set of threeinput terminals for receiving said third, fourth and fifth controlsignals, respectively, and outputting a signal corresponding to a signalobtained by dividing each of said third, fourth and fifth controlsignals based on a resistance of each of nodes at which transistorcircuits composing said first differential amplification circuit andeach of said first set of input terminals are commonly connected; and aMAX circuit including a second differential amplification circuit with asecond set of three input terminals for receiving said first controlsignal, said second control signal and the signal outputted from saidMIN circuit, and outputting a signal corresponding to a signal obtainedby dividing each of said first control signal, said second controlsignal and the signal outputted from said MIN circuit based on aresistance of each of other nodes at which other transistor circuitscomposing said second differential amplification circuit and each ofsaid second set of input terminals are commonly connected, and whereinsaid control signal outputted from said control circuit is said signaloutputted from said MAX circuit.
 18. A crystal oscillation device ofclaim 9, wherein said storage means comprises: a RAM data input circuit;a ROM circuit; and a switch circuit, said RAM data input circuitperforming a parallel conversion on a serial data received from outsidebased on a clock signal when an operation enable signal indicates thatoperation is permitted, to generate a plurality of parallel data, andoutputting said parallel data to said ROM circuit and said switchcircuit; a PROM circuit storing said parallel data received from saidRAM data input circuit at a data storage circuit included in said PROMcircuit when a read/write control signal indicates that write operationis permitted, while outputting said parallel data to said switch circuitwhen said read/write control signal indicates that read operation ispermitted; and said switch circuit selecting either of said paralleldata outputted from said RAM data input circuit and from said PROMcircuit, and outputting said selected parallel data.
 19. A method ofadjusting a crystal oscillation device including a first analog signalgenerating circuit for generating and outputting a predetermined analogsignal substantially independent of an ambient temperature; a secondanalog signal generating circuit for generating and outputting an analogsignal dependent upon the ambient temperature; a control circuit forreceiving said signal from said first analog signal generating circuitand said signal from said second analog signal generating circuit, andfor generating, with a feasible range of the ambient temperaturecontinuously divided into a first temperature region, a secondtemperature region, a third temperature region, a fourth temperatureregion and a fifth temperature region in this order along a directionfrom a low temperature to a high temperature, control signalsrespectively corresponding to said five temperature regions; a crystaloscillating circuit for receiving a control signal from said controlcircuit so as to be controlled to have an oscillation frequency at apredetermined value by said control signal; a RAM circuit for storingparameters, for compensating a temperature dependency of the oscillationfrequency of said crystal oscillating circuit, of said first throughfifth control signals output by said control circuit, with varying eachof said parameters with regard to each of said control signals; and aprogrammable ROM circuit for storing an optimal parameter of saidparameters with regard to each of said control signals, said controlcircuit outputting a first control signal whose output value isdecreased in proportion to increase of the temperature when the ambienttemperature is in said first temperature region; a second control signalwhose output value is continuous with said first control signal and is apredetermined value independent of the temperature when the ambienttemperature is in said second temperature region; a third control signalwhose output value is continuous with said second control signal and isincreased in proportion to increase of the temperature when the ambienttemperature is in said third temperature region; a fourth control signalwhose output value is continuous with said third control signal and is apredetermined value independent of the temperature when the ambienttemperature is in said fourth temperature region; and a fifth controlsignal whose output value is continuous with said fourth control signaland is decreased in proportion to increase of the temperature when theambient temperature is in said fifth temperature region, said methodcomprising: a peculiar parameter determining step of determiningpeculiar parameters by allowing said crystal oscillation device to standat a temperature continuously varying from said first temperature regionto said fifth temperature region and by calculating parameters of saidcontrol signals respectively corresponding to a cubic temperaturecoefficient, a linear temperature coefficient, a frequency differencefrom a reference frequency at a temperature of an inflection point andsaid temperature of the inflection point of the temperaturecharacteristic of said crystal oscillating circuit so as to makevariation of the oscillation frequency output by said crystaloscillating circuit caused by the temperature substantially zero; aninitial parameter determining step of determining initial parameters bymeasuring an initial temperature characteristic of said control signalsoutput by said control circuit and by calculating the parameters of saidcontrol signals respectively corresponding to said cubic temperaturecoefficient, said linear temperature coefficient, said frequencydifference from the reference frequency at said temperature of theinflection point and said temperature of the inflection point; and anoptimal parameter writing step of obtaining change amounts of saidcontrol signals per unit of data corresponding to temperaturecompensating parameters stored in said RAM circuit by measuring a changeamount of said initial temperature characteristic with changing saiddata corresponding to said temperature compensating parameters,obtaining differences between said initial parameters and said peculiarparameters, determining an optimal parameter of said control signals soas to minimize said differences on the basis of said change amounts ofsaid control signals per unit of said data, and writing said optimalparameter in said ROM circuit.
 20. A method of adjusting a crystaloscillation device including a first analog signal generating circuitfor generating and outputting a predetermined analog signalsubstantially independent of an ambient temperature; a second analogsignal generating circuit for generating and outputting an analog signaldependent upon the ambient temperature; a control circuit for receivingsaid signal from said first analog signal generating circuit and saidsignal from said second analog signal generating circuit, and forgenerating, with a feasible range of the ambient temperaturecontinuously divided into a first temperature region, a secondtemperature region, a third temperature region, a fourth temperatureregion and a fifth temperature region in this order along a directionfrom a low temperature to a high temperature, control signalsrespectively corresponding to said five temperature regions; a crystaloscillating circuit for receiving a control signal from said controlcircuit so as to be controlled to have an oscillation frequency at apredetermined value by said control signal; a RAM circuit for storingparameters, for compensating a temperature dependency of the oscillationfrequency of said crystal oscillating circuit, of said first throughfifth control signals output by said control circuit, with varying eachof said parameters with regard to each of said control signals; and aprogrammable ROM circuit for storing an optimal parameter of saidparameters with regard to each of said control signals, said controlcircuit outputting a first control signal whose output value isdecreased in proportion to increase of the temperature when the ambienttemperature is in said first temperature region; a second control signalwhose output value is continuous with said first control signal and is apredetermined value independent of the temperature when the ambienttemperature is in said second temperature region; a third control signalwhose output value is continuous with said second control signal and isincreased in proportion to increase of the temperature when the ambienttemperature is in said third temperature region; a fourth control signalwhose output value is continuous with said third control signal and is apredetermined value independent of the temperature when the ambienttemperature is in said fourth temperature region; and a fifth controlsignal whose output value is continuous with said fourth control signaland is decreased in proportion to increase of the temperature when theambient temperature is in said fifth temperature region, said methodcomprising: a peculiar control voltage measuring step of measuring apeculiar control voltage which reduces variation of the oscillationfrequency output by said crystal oscillating circuit caused by thetemperature to about zero, by allowing said crystal oscillation deviceto stand at a temperature continuously varying from said firsttemperature region to said fifth temperature region; a peculiarparameter determining step of determining peculiar parametersrespectively corresponding to a cubic temperature coefficient, a lineartemperature coefficient, a frequency difference from a referencefrequency at a temperature of an inflection point and said temperatureof the inflection point of the temperature characteristic of a crystaloscillator in said crystal oscillating circuit, based on temperaturecharacteristic of said peculiar control voltage; an initial controlvoltage characteristic measuring step of measuring temperaturecharacteristic of an initial control voltage of said control circuit bychanging temperature compensating parameters received by and stored insaid RAM circuit; an initial parameter determining step of determininginitial parameters based on said temperature characteristic of saidinitial control voltage by calculating parameters of said controlsignals respectively corresponding to said cubic temperaturecoefficient, said linear temperature coefficient, said frequencydifference from the reference frequency at said temperature of theinflection point and said temperature of the inflection point of saidcrystal oscillator in said crystal oscillation circuit; a change amountcalculating step of calculating by bit, change amounts of saidtemperature compensating parameters stored in said RAM circuit; adifference calculating step of calculating differences between saidpeculiar parameters and said initial parameters; and an optimalparameter determining step of determining an optimal parameter whichreduces said differences to about zero, based on said change amountscalculated by bit.
 21. A function generator comprising: a first analogsignal generating circuit for generating and outputting a predeterminedanalog signal substantially independent of an ambient temperature; asecond analog signal generating circuit for generating and outputting ananalog signal dependent upon the ambient temperature; a control circuitfor receiving said signal from said first analog signal generatingcircuit and said signal from said second analog signal generatingcircuit, and for generating and outputting, with a feasible range of theambient temperature continuously divided into a first temperatureregion, a second temperature region, a third temperature region, afourth temperature region and a fifth temperature region in this orderalong a direction from a low temperature to a high temperature, controlsignals respectively corresponding to said five temperature regions,wherein said function generator selects any of said control signals andgenerates a control signal serving as a function of a temperature fromthe selected signal, and wherein said control circuit comprises: a firstcontrol signal generating circuit for outputting a first control signalwhose output value is varied in proportion to increase of thetemperature at a first change rate when the ambient temperature is insaid first temperature region; a second control signal generatingcircuit for outputting a second control signal whose output value is apredetermined value independent of the temperature when the ambienttemperature is in said second temperature region; a third control signalgenerating circuit for outputting a third control signal whose outputvalue is varied in proportion to increase of the temperature at a secondchange rate when the ambient temperature is in said third temperatureregion; a fourth control signal generating circuit for outputting afourth control signal whose output value is a predetermined valueindependent of the temperature when the ambient temperature is in saidfourth temperature region; a fifth control signal generating circuit foroutputting a fifth control signal whose output value is varied inproportion to increase of the temperature at a third change rate; amaximum value signal output circuit for receiving said first, second andthird control signals and outputting as a maximum value signal, any ofsaid first, second and third control signals, whichever has a maximumvalue; and a minimum value signal output circuit for receiving saidmaximum value signal, said fourth control signal, and said fifth controlsignal, and outputting as a minimum value signal, any of said maximumvalue signal, said fourth control signal and said fifth control signal,whichever has a minimum value, and wherein said control signal generatedby said function generator is said minimum value signal.
 22. A functiongenerator comprising: a first analog signal generating circuit forgenerating and outputting a predetermined analog signal substantiallyindependent of an ambient temperature; a second analog signal generatingcircuit for generating and outputting an analog signal dependent uponthe ambient temperature; a control circuit for receiving said signalfrom said first analog signal generating circuit and said signal fromsaid second analog signal generating circuit, and for generating andoutputting, with a feasible range of the ambient temperaturecontinuously divided into a first temperature region, a secondtemperature region, a third temperature region, a fourth temperatureregion and a fifth temperature region in this order along a directionfrom a low temperature to a high temperature, control signalsrespectively corresponding to said five temperature regions, whereinsaid function generator selects any of said control signals andgenerates a control signal as a function of a temperature from theselected signal, and wherein said control circuit comprises: a firstcontrol signal generating circuit for outputting a first control signalwhose output value is varied in proportion to increase of thetemperature at a first change rate when the ambient temperature is insaid first temperature region; a second control signal generatingcircuit for outputting a second control signal whose output value is apredetermined value independent of the temperature when the ambienttemperature is in said second temperature region; a third control signalgenerating circuit for outputting a third control signal whose outputvalue is varied in proportion to increase of the temperature at a secondchange rate when the ambient temperature is in said third temperatureregion; a fourth control signal generating circuit for outputting afourth control signal whose output value is a predetermined valueindependent of the temperature when the ambient temperature is in saidfourth temperature region; a fifth control signal generating circuit foroutputting a fifth control signal whose output value is varied inproportion to increase of the temperature at a third change rate; aminimum value signal output circuit for receiving said third, fourth andfifth control signals and outputting as a minimum value signal, any ofsaid third, fourth and fifth control signals, whichever has a minimumvalue; and a maximum value signal output circuit for receiving saidminimum value signal, said first control signal, and said second controlsignal, and outputting as a maximum value signal, any of said minimumvalue signal, said first control signal, and said second control signal,whichever has a maximum value, and wherein said control signal outputtedfrom said control circuit is said maximum value signal.
 23. A crystaloscillator comprising: a first analog signal generating circuit forgenerating and outputting a predetermined analog signal substantiallyindependent of an ambient temperature; a second analog signal generatingcircuit for generating and outputting an analog signal dependent uponthe ambient temperature; a control circuit for receiving said signalfrom said first analog signal generating circuit and said signal fromsaid second analog signal generating circuit, and for generating andoutputting, with a feasible range of the ambient temperaturecontinuously divided into a first temperature region, a secondtemperature region, a third temperature region, a fourth temperatureregion and a fifth temperature region in this order along a directionfrom a low temperature to a high temperature, control signalsrespectively corresponding to said five temperature regions; and acrystal oscillation circuit for receiving a control signal from saidcontrol circuit so as to be controlled to have an oscillation frequencyat a predetermined value by said control signal, wherein said controlcircuit selects any of said control signals and generates a controlsignal serving as a function of a temperature from the selected signal,and wherein said control circuit comprises: a first control signalgenerating circuit for outputting a first control signal whose outputvalue is varied in proportion to increase of the temperature at a firstchange rate when the ambient temperature is in said first temperatureregion; a second control signal generating circuit for outputting asecond control signal whose output value is a predetermined valueindependent of the temperature when the ambient temperature is in saidsecond temperature region; a third control signal generating circuit foroutputting a third control signal whose output value is varied inproportion to increase of the temperature at a second change rate whenthe ambient temperature is in said third temperature region; a fourthcontrol signal generating circuit for outputting a fourth control signalwhose output value is a predetermined value independent of thetemperature when the ambient temperature is in said fourth temperatureregion; a fifth control signal generating circuit for outputting a fifthcontrol signal whose output value is varied in proportion to increase ofthe temperature at a third change rate; a maximum value signal outputcircuit for receiving said first, second and third control signals andoutputting as a maximum value signal, any of said first, second andthird control signals, whichever has a maximum value; and a minimumvalue signal output circuit for receiving said meaximum value signal,said fourth control signal, and said fifth control signal, andoutputting as a minimum value signal, any of said maximum value signal,said fourth control signal and said fifth control signal, whichever hasa minimum value, and wherein said control signal generated by saidfunction generator is said minimum value signal.
 24. A crystaloscillation circuit comprising: a first analog signal generating circuitfor generating and outputting a predetermined analog signalsubstantially independent of an ambient temperature; a second analogsignal generating circuit for generating and outputting an analog signaldependent upon the ambient temperature; a control circuit for receivingsaid signal from said first analog signal generating circuit and saidsignal from said second analog signal generating circuit, and forgenerating and outputting, with a feasible range of the ambienttemperature continuously divided into a first temperature region, asecond temperature region, a third temperature region, a fourthtemperature region and a fifth temperature region in this order along adirection from a low temperature to a high temperature, control signalsrespectively corresponding to said five temperature regions; and acrystal oscillation circuit for receiving a control signal from saidcontrol circuit so as to be controlled to have an oscillation frequencyat a predetermined value by said control signal, wherein said controlcircuit selects any of said control signals and generates a controlsignal as a function of a temperature from the selected signal, andwherein said control circuit comprises: a first control signalgenerating circuit for outputting a first control signal whose outputvalue is varied in proportion to increase of the temperature at a firstchange rate when the ambient temperature is in said first temperatureregion; a second control signal generating circuit for outputting asecond control signal whose output value is a predetermined valueindependent of the temperature when the ambient temperature is in saidsecond temperature region; a third control signal generating circuit foroutputting a third control signal whose output value is varied inproportion to increase of the temperature at a second change rate whenthe ambient temperature is in said third temperature region; a fourthcontrol signal generating circuit for outputting a fourth control signalwhose output value is a predetermined value independent of thetemperature when the ambient temperature is in said fourth temperatureregion; a fifth control signal generating circuit for outputting a fifthcontrol signal whose output value is varied in proportion to increase ofthe temperature at a third change rate; a minimum value signal outputcircuit for receiving said third, fourth and fifth control signals andoutputting as a minimum value signal, any of said third, fourth andfifth control signals, whichever has a minimum value; and a maximumvalue signal output circuit for receiving said minimum value signal,said first control signal, and said second control signal, andoutputting as a maximum value signal, any of said minimum value signal,said first control signal, and said second control signal, whichever hasa maximum value, and wherein said control signal generated by saidcontrol circuit is said maximum value signal.
 25. A function generatorcomprising: a first analog signal generating circuit for generating andoutputting a predetermined analog signal substantially independent of anambient temperature; storage means for storing control informationrespectively corresponding to first, second and third temperatureregions obtained by dividing a feasible range of the ambient temperatureinto three continuous parts in this order along a direction from a lowtemperature to a high temperature; a second analog signal generatingcircuit for receiving said signal from said first analog signalgenerating circuit and said control information from said storage means,and for generating and outputting first, second and third controlsignals respectively corresponding to said three temperature regions;and a control circuit for receiving said first through third controlsignals and generating to output a control signal as a function of atemperature based on each received signal, wherein said storage meansstores as said control information: a first proportional value defininga relationship between a proportional coefficient between a temperatureused for generating said first control signal and the output valuethereof and a cubic coefficient of a temperature characteristic of anoscillation frequency of a quartz oscillator; a second proportionalvalue defining a relationship between a proportional coefficient betweena temperature used for generating said second control signal and theoutput value thereof and said cubic coefficient; a third proportionalvalue defining a relationship between a proportional coefficient betweena temperature used for generating said third control signal and the output value thereof and said cubic coefficient, wherein said controlcircuit comprises: a MAX circuit receiving said first and second controlsignals, and outputting either of said first and second control signals,whichever has a maximum value at a given temperature within either ofsaid first and second temperature regions; and a MIN circuit receivingsaid third control signal and the signal outputted from said MAXcircuit, and outputting either of said third control signal and thesignal outputted from said MAX circuit, whichever has a minimum value ata given temperature within said third temperature region, and whereinsaid control signal outputted from said control circuit is the signaloutputted from said MIN circuit.
 26. A function generator of claim 25,wherein said control circuit comprises: a MAX circuit including a firstdifferential amplification circuit with a first set of two inputterminals for receiving said first and second control signals,respectively, and outputting a signal corresponding to a signal obtainedby dividing each of said first and second control signals based on aresistance of each of nodes at which transistor circuits composing saidfirst differential amplification circuit and each of said first set ofinput terminals are commonly connected; and a MIN circuit including asecond differential amplification circuit with a second set of two inputterminals for receiving said third control signal and the signaloutputted from said MAX circuit, and outputting a signal correspondingto a signal obtained by dividing each of said third control signal andthe signal outputted from said MAX circuit based on a resistance of eachof other nodes at which other transistor circuits composing said seconddifferential amplification circuit and each of said second set of inputterminals are commonly connected, and wherein said control signaloutputted from said control circuit is said signal outputted from saidMIN circuit.
 27. A function generator of claim 25, wherein said controlcircuit comprises: a MIN circuit receiving said second and third controlsignals, and outputting either of said second and third control signals,whichever has a minimum value at a given temperature in either of saidsecond and third temperature regions; and a MAX circuit receiving saidfirst control signal and the signal outputted from said MIN circuit, andoutputting either of said first control signal and the signal outputtedfrom said MIN circuit, whichever has a maximum value at a giventemperature within said first temperature region, and wherein saidcontrol signal outputted from said control circuit is the signaloutputted from said MAX circuit.
 28. A function generator of claim 25,wherein said control circuit comprises: a MIN circuit including a firstdifferential amplification circuit with a first set of two inputterminals for receiving said second and third control signals,respectively, and outputting a signal corresponding to a signal obtainedby dividing each of said second and third control signals based on aresistance of each nodes at which transistor circuits composing saidfirst differential amplification circuit and each of said first set ofinput terminals are commonly connected; and a MAX circuit including asecond differential amplification circuit with a second set of two inputterminals for receiving said first control signal and the signaloutputted from said MAX circuit, and outputting a signal correspondingto a signal obtained by dividing each of said first control signal andthe signal outputted from said MAX circuit based on a resistance of eachof other nodes at which other transistor circuits composing said seconddifferential amplification circuit and each of said second set of inputterminals are commonly connected, and wherein said control signaloutputted from said control circuit is the signal outputted from saidMAX circuit.